Merge remote-tracking branch 'origin/5.12' into dev

Change-Id: If28421324777e5165f63c9f856cb6d133709c799

48 files changed, 809 insertions, 620 deletions

diff --git a/src/qml/compiler/qv4bytecodehandler.cpp b/src/qml/compiler/qv4bytecodehandler.cpp
index e2533a0505..181594010d 100644
--- a/src/qml/compiler/qv4bytecodehandler.cpp
+++ b/src/qml/compiler/qv4bytecodehandler.cpp
@@ -290,6 +290,9 @@ std::vector<int> ByteCodeHandler::collectLabelsInBytecode(const char *code, uint
             addLabel(code - start + offset);
         COLLECTOR_END_INSTR(UnwindToLabel)
 
+        COLLECTOR_BEGIN_INSTR(DeadTemporalZoneCheck)
+        COLLECTOR_END_INSTR(DeadTemporalZoneCheck)
+
         COLLECTOR_BEGIN_INSTR(ThrowException)
         COLLECTOR_END_INSTR(ThrowException)
 
@@ -519,6 +522,9 @@ std::vector<int> ByteCodeHandler::collectLabelsInBytecode(const char *code, uint
         COLLECTOR_END_INSTR(Debug)
 #endif // QT_NO_QML_DEBUGGER
 
+        COLLECTOR_BEGIN_INSTR(InitializeBlockDeadTemporalZone)
+        COLLECTOR_END_INSTR(InitializeBlockDeadTemporalZone)
+
         COLLECTOR_BEGIN_INSTR(LoadQmlContext)
         COLLECTOR_END_INSTR(LoadQmlContext)
 
diff --git a/src/qml/compiler/qv4codegen.cpp b/src/qml/compiler/qv4codegen.cpp
index 734de853d1..412d787d11 100644
--- a/src/qml/compiler/qv4codegen.cpp
+++ b/src/qml/compiler/qv4codegen.cpp
@@ -47,6 +47,7 @@
 #include <QtCore/QBitArray>
 #include <QtCore/QLinkedList>
 #include <QtCore/QStack>
+#include <QScopeGuard>
 #include <private/qqmljsast_p.h>
 #include <private/qv4string_p.h>
 #include <private/qv4value_p.h>
@@ -501,8 +502,14 @@ void Codegen::variableDeclaration(PatternElement *ast)
 {
     RegisterScope scope(this);
 
-    if (!ast->initializer)
+    if (!ast->initializer) {
+        if (ast->isLexicallyScoped()) {
+            Reference::fromConst(this, Encode::undefined()).loadInAccumulator();
+            Reference varToStore = targetForPatternElement(ast);
+            varToStore.storeConsumeAccumulator();
+        }
         return;
+    }
     initializeAndDestructureBindingElement(ast, Reference(), /*isDefinition*/ true);
 }
 
@@ -516,7 +523,7 @@ void Codegen::variableDeclarationList(VariableDeclarationList *ast)
 Codegen::Reference Codegen::targetForPatternElement(AST::PatternElement *p)
 {
     if (!p->bindingIdentifier.isNull())
-        return referenceForName(p->bindingIdentifier.toString(), true);
+        return referenceForName(p->bindingIdentifier.toString(), true, p->firstSourceLocation());
     if (!p->bindingTarget || p->destructuringPattern())
         return Codegen::Reference::fromStackSlot(this);
     Reference lhs = expression(p->bindingTarget);
@@ -2235,9 +2242,9 @@ bool Codegen::visit(FunctionExpression *ast)
     return false;
 }
 
-Codegen::Reference Codegen::referenceForName(const QString &name, bool isLhs)
+Codegen::Reference Codegen::referenceForName(const QString &name, bool isLhs, const SourceLocation &accessLocation)
 {
-    Context::ResolvedName resolved = _context->resolveName(name);
+    Context::ResolvedName resolved = _context->resolveName(name, accessLocation);
 
     if (resolved.type == Context::ResolvedName::Local || resolved.type == Context::ResolvedName::Stack
         || resolved.type == Context::ResolvedName::Import) {
@@ -2258,6 +2265,8 @@ Codegen::Reference Codegen::referenceForName(const QString &name, bool isLhs)
             r.isVolatile = true;
         r.isArgOrEval = resolved.isArgOrEval;
         r.isReferenceToConst = resolved.isConst;
+        r.requiresTDZCheck = resolved.requiresTDZCheck;
+        r.name = name; // used to show correct name at run-time when TDZ check fails.
         return r;
     }
 
@@ -2293,7 +2302,7 @@ bool Codegen::visit(IdentifierExpression *ast)
     if (hasError)
         return false;
 
-    _expr.setResult(referenceForName(ast->name.toString(), false));
+    _expr.setResult(referenceForName(ast->name.toString(), false, ast->firstSourceLocation()));
     return false;
 }
 
@@ -2321,11 +2330,10 @@ void Codegen::handleConstruct(const Reference &base, ArgumentList *arguments)
     if (hasError)
         return;
 
-    if (base.isSuper()) {
-        Reference::fromStackSlot(this, CallData::Function).loadInAccumulator();
-    } else {
+    if (base.isSuper())
+        Reference::fromStackSlot(this, CallData::NewTarget).loadInAccumulator();
+    else
         constructor.loadInAccumulator();
-    }
 
     if (calldata.hasSpread) {
         Instruction::ConstructWithSpread create;
@@ -3102,7 +3110,7 @@ bool Codegen::visit(ForEachStatement *ast)
     Reference lhsValue = Reference::fromStackSlot(this);
 
     // There should be a temporal block, so that variables declared in lhs shadow outside vars.
-    // This block should define a temporal dead zone for those variables, which is not yet implemented.
+    // This block should define a temporal dead zone for those variables.
     {
         RegisterScope innerScope(this);
         ControlFlowBlock controlFlow(this, ast);
@@ -3818,7 +3826,7 @@ Codegen::Reference &Codegen::Reference::operator =(const Reference &other)
         scope = other.scope;
         break;
     case Name:
-        name = other.name;
+        // name is always copied
         break;
     case Member:
         propertyBase = other.propertyBase;
@@ -3848,6 +3856,8 @@ Codegen::Reference &Codegen::Reference::operator =(const Reference &other)
     codegen = other.codegen;
     isReadonly = other.isReadonly;
     isReferenceToConst = other.isReferenceToConst;
+    name = other.name;
+    requiresTDZCheck = other.requiresTDZCheck;
     stackSlotIsLocalOrArgument = other.stackSlotIsLocalOrArgument;
     isVolatile = other.isVolatile;
     global = other.global;
@@ -3969,10 +3979,10 @@ void Codegen::Reference::storeOnStack(int slotIndex) const
 
 Codegen::Reference Codegen::Reference::doStoreOnStack(int slotIndex) const
 {
-    if (isStackSlot() && slotIndex == -1 && !(stackSlotIsLocalOrArgument && isVolatile))
+    if (isStackSlot() && slotIndex == -1 && !(stackSlotIsLocalOrArgument && isVolatile) && !requiresTDZCheck)
         return *this;
 
-    if (isStackSlot()) { // temp-to-temp move
+    if (isStackSlot() && !requiresTDZCheck) { // temp-to-temp move
         Reference dest = Reference::fromStackSlot(codegen, slotIndex);
         Instruction::MoveReg move;
         move.srcReg = stackSlot();
@@ -4130,6 +4140,22 @@ void Codegen::Reference::storeAccumulator() const
 
 void Codegen::Reference::loadInAccumulator() const
 {
+    auto tdzCheck = [this](bool requiresCheck){
+        if (!requiresCheck)
+            return;
+        Instruction::DeadTemporalZoneCheck check;
+        check.name = codegen->registerString(name);
+        codegen->bytecodeGenerator->addInstruction(check);
+    };
+    auto tdzCheckStackSlot = [this, tdzCheck](Moth::StackSlot slot, bool requiresCheck){
+        if (!requiresCheck)
+            return;
+        Instruction::LoadReg load;
+        load.reg = slot;
+        codegen->bytecodeGenerator->addInstruction(load);
+        tdzCheck(true);
+    };
+
     switch (type) {
     case Accumulator:
         return;
@@ -4137,6 +4163,7 @@ void Codegen::Reference::loadInAccumulator() const
         Q_UNREACHABLE();
         return;
     case SuperProperty:
+        tdzCheckStackSlot(property, subscriptRequiresTDZCheck);
         Instruction::LoadSuperProperty load;
         load.property = property.stackSlot();
         codegen->bytecodeGenerator->addInstruction(load);
@@ -4183,6 +4210,7 @@ QT_WARNING_POP
         Instruction::LoadReg load;
         load.reg = stackSlot();
         codegen->bytecodeGenerator->addInstruction(load);
+        tdzCheck(requiresTDZCheck);
     } return;
     case ScopedLocal: {
         if (!scope) {
@@ -4195,6 +4223,7 @@ QT_WARNING_POP
             load.scope = scope;
             codegen->bytecodeGenerator->addInstruction(load);
         }
+        tdzCheck(requiresTDZCheck);
         return;
     }
     case Name:
@@ -4223,13 +4252,13 @@ QT_WARNING_POP
         }
         return;
     case Member:
+        propertyBase.loadInAccumulator();
+        tdzCheck(requiresTDZCheck);
         if (!disable_lookups && codegen->useFastLookups) {
-            propertyBase.loadInAccumulator();
             Instruction::GetLookup load;
             load.index = codegen->registerGetterLookup(propertyNameIndex);
             codegen->bytecodeGenerator->addInstruction(load);
         } else {
-            propertyBase.loadInAccumulator();
             Instruction::LoadProperty load;
             load.name = propertyNameIndex;
             codegen->bytecodeGenerator->addInstruction(load);
@@ -4239,9 +4268,12 @@ QT_WARNING_POP
         Instruction::LoadImport load;
         load.index = index;
         codegen->bytecodeGenerator->addInstruction(load);
+        tdzCheck(requiresTDZCheck);
     } return;
     case Subscript: {
+        tdzCheckStackSlot(elementBase, requiresTDZCheck);
         elementSubscript.loadInAccumulator();
+        tdzCheck(subscriptRequiresTDZCheck);
         Instruction::LoadElement load;
         load.base = elementBase;
         codegen->bytecodeGenerator->addInstruction(load);
diff --git a/src/qml/compiler/qv4codegen_p.h b/src/qml/compiler/qv4codegen_p.h
index 516f506396..adea8b3009 100644
--- a/src/qml/compiler/qv4codegen_p.h
+++ b/src/qml/compiler/qv4codegen_p.h
@@ -217,9 +217,10 @@ public:
             case Name:
             case Member:
             case Subscript:
+            case SuperProperty:
                 return true;
             default:
-                return false;
+                return requiresTDZCheck;
             }
         }
         bool isConstant() const { return type == Const; }
@@ -294,12 +295,14 @@ public:
             Reference r(baseRef.codegen, Member);
             r.propertyBase = baseRef.asRValue();
             r.propertyNameIndex = r.codegen->registerString(name);
+            r.requiresTDZCheck = baseRef.requiresTDZCheck;
             return r;
         }
         static Reference fromSuperProperty(const Reference &property) {
             Q_ASSERT(property.isStackSlot());
             Reference r(property.codegen, SuperProperty);
             r.property = property.stackSlot();
+            r.subscriptRequiresTDZCheck = property.requiresTDZCheck;
             return r;
         }
         static Reference fromSubscript(const Reference &baseRef, const Reference &subscript) {
@@ -307,6 +310,8 @@ public:
             Reference r(baseRef.codegen, Subscript);
             r.elementBase = baseRef.stackSlot();
             r.elementSubscript = subscript.asRValue();
+            r.requiresTDZCheck = baseRef.requiresTDZCheck;
+            r.subscriptRequiresTDZCheck = subscript.requiresTDZCheck;
             return r;
         }
         static Reference fromConst(Codegen *cg, QV4::ReturnedValue constant) {
@@ -334,6 +339,9 @@ public:
         static Reference fromThis(Codegen *cg) {
             Reference r = fromStackSlot(cg, CallData::This);
             r.isReadonly = true;
+            // ### Optimize this. Functions that are not derived constructors or arrow functions can't have an
+            // empty this object
+            r.requiresTDZCheck = true;
             return r;
         }
 
@@ -394,6 +402,8 @@ public:
         mutable bool isArgOrEval = false;
         bool isReadonly = false;
         bool isReferenceToConst = false;
+        bool requiresTDZCheck = false;
+        bool subscriptRequiresTDZCheck = false;
         bool stackSlotIsLocalOrArgument = false;
         bool isVolatile = false;
         bool global = false;
@@ -684,7 +694,7 @@ public:
     void handleTryFinally(AST::TryStatement *ast);
 
 
-    Reference referenceForName(const QString &name, bool lhs);
+    Reference referenceForName(const QString &name, bool lhs, const QQmlJS::AST::SourceLocation &accessLocation = QQmlJS::AST::SourceLocation());
 
     QQmlRefPointer<QV4::CompiledData::CompilationUnit> generateCompilationUnit(bool generateUnitData = true);
     static QQmlRefPointer<QV4::CompiledData::CompilationUnit> createUnitForLoading();
diff --git a/src/qml/compiler/qv4compileddata_p.h b/src/qml/compiler/qv4compileddata_p.h
index dca38eae54..1f6c591ada 100644
--- a/src/qml/compiler/qv4compileddata_p.h
+++ b/src/qml/compiler/qv4compileddata_p.h
@@ -237,6 +237,8 @@ struct Block
 {
     quint32_le nLocals;
     quint32_le localsOffset;
+    quint16_le sizeOfLocalTemporalDeadZone;
+    quint16_le padding;
 
     const quint32_le *localsTable() const { return reinterpret_cast<const quint32_le *>(reinterpret_cast<const char *>(this) + localsOffset); }
 
@@ -251,7 +253,7 @@ struct Block
         return (a + 7) & ~size_t(7);
     }
 };
-static_assert(sizeof(Block) == 8, "Block structure needs to have the expected size to be binary compatible on disk when generated by host compiler and loaded by target");
+static_assert(sizeof(Block) == 12, "Block structure needs to have the expected size to be binary compatible on disk when generated by host compiler and loaded by target");
 
 // Function is aligned on an 8-byte boundary to make sure there are no bus errors or penalties
 // for unaligned access. The ordering of the fields is also from largest to smallest.
@@ -276,6 +278,10 @@ struct Function
     quint16_le nLineNumbers;
     size_t lineNumberOffset() const { return localsOffset + nLocals * sizeof(quint32); }
     quint32_le nestedFunctionIndex; // for functions that only return a single closure, used in signal handlers
+    quint16_le sizeOfLocalTemporalDeadZone;
+    quint16_le firstTemporalDeadZoneRegister;
+    quint16_le sizeOfRegisterTemporalDeadZone;
+    quint16_le nRegisters;
     Location location;
 
     // Qml Extensions Begin
@@ -293,7 +299,6 @@ struct Function
     // Keep all unaligned data at the end
     quint8 flags;
     quint8 padding1;
-    quint16_le nRegisters;
 
     //    quint32 formalsIndex[nFormals]
     //    quint32 localsIndex[nLocals]
@@ -326,7 +331,7 @@ struct Function
         return (a + 7) & ~size_t(7);
     }
 };
-static_assert(sizeof(Function) == 48, "Function structure needs to have the expected size to be binary compatible on disk when generated by host compiler and loaded by target");
+static_assert(sizeof(Function) == 52, "Function structure needs to have the expected size to be binary compatible on disk when generated by host compiler and loaded by target");
 
 struct Method {
     enum Type {
diff --git a/src/qml/compiler/qv4compiler.cpp b/src/qml/compiler/qv4compiler.cpp
index 4a726c366d..b6e5504c24 100644
--- a/src/qml/compiler/qv4compiler.cpp
+++ b/src/qml/compiler/qv4compiler.cpp
@@ -398,6 +398,10 @@ void QV4::Compiler::JSUnitGenerator::writeFunction(char *f, QV4::Compiler::Conte
     function->formalsOffset = currentOffset;
     currentOffset += function->nFormals * sizeof(quint32);
 
+    function->sizeOfLocalTemporalDeadZone = irFunction->sizeOfLocalTemporalDeadZone;
+    function->sizeOfRegisterTemporalDeadZone = irFunction->sizeOfRegisterTemporalDeadZone;
+    function->firstTemporalDeadZoneRegister = irFunction->firstTemporalDeadZoneRegister;
+
     function->nLocals = irFunction->locals.size();
     function->localsOffset = currentOffset;
     currentOffset += function->nLocals * sizeof(quint32);
@@ -532,6 +536,7 @@ void QV4::Compiler::JSUnitGenerator::writeBlock(char *b, QV4::Compiler::Context
     quint32 currentOffset = sizeof(QV4::CompiledData::Block);
     currentOffset = (currentOffset + 7) & ~quint32(0x7);
 
+    block->sizeOfLocalTemporalDeadZone = irBlock->sizeOfLocalTemporalDeadZone;
     block->nLocals = irBlock->locals.size();
     block->localsOffset = currentOffset;
     currentOffset += block->nLocals * sizeof(quint32);
diff --git a/src/qml/compiler/qv4compilercontext.cpp b/src/qml/compiler/qv4compilercontext.cpp
index 09be19e427..4ee6d2c179 100644
--- a/src/qml/compiler/qv4compilercontext.cpp
+++ b/src/qml/compiler/qv4compilercontext.cpp
@@ -71,7 +71,22 @@ Context *Module::newContext(Node *node, Context *parent, ContextType contextType
     return c;
 }
 
-bool Context::addLocalVar(const QString &name, Context::MemberType type, VariableScope scope, FunctionExpression *function)
+bool Context::Member::requiresTDZCheck(const SourceLocation &accessLocation, bool accessAcrossContextBoundaries) const
+{
+    if (!isLexicallyScoped())
+        return false;
+
+    if (accessAcrossContextBoundaries)
+        return true;
+
+    if (!accessLocation.isValid() || !endOfInitializerLocation.isValid())
+        return true;
+
+    return accessLocation.begin() < endOfInitializerLocation.end();
+}
+
+bool Context::addLocalVar(const QString &name, Context::MemberType type, VariableScope scope, FunctionExpression *function,
+                          const QQmlJS::AST::SourceLocation &endOfInitializer)
 {
     // ### can this happen?
     if (name.isEmpty())
@@ -96,17 +111,18 @@ bool Context::addLocalVar(const QString &name, Context::MemberType type, Variabl
 
     // hoist var declarations to the function level
     if (contextType == ContextType::Block && (scope == VariableScope::Var && type != MemberType::FunctionDefinition))
-        return parent->addLocalVar(name, type, scope, function);
+        return parent->addLocalVar(name, type, scope, function, endOfInitializer);
 
     Member m;
     m.type = type;
     m.function = function;
     m.scope = scope;
+    m.endOfInitializerLocation = endOfInitializer;
     members.insert(name, m);
     return true;
 }
 
-Context::ResolvedName Context::resolveName(const QString &name)
+Context::ResolvedName Context::resolveName(const QString &name, const QQmlJS::AST::SourceLocation &accessLocation)
 {
     int scope = 0;
     Context *c = this;
@@ -126,6 +142,7 @@ Context::ResolvedName Context::resolveName(const QString &name)
             result.scope = scope;
             result.index = m.index;
             result.isConst = (m.scope == VariableScope::Const);
+            result.requiresTDZCheck = m.requiresTDZCheck(accessLocation, c != this);
             if (c->isStrict && (name == QLatin1String("arguments") || name == QLatin1String("eval")))
                 result.isArgOrEval = true;
             return result;
@@ -162,6 +179,8 @@ Context::ResolvedName Context::resolveName(const QString &name)
                 result.index = i;
                 result.type = ResolvedName::Import;
                 result.isConst = true;
+                // We don't know at compile time whether the imported value is let/const or not.
+                result.requiresTDZCheck = true;
                 return result;
             }
         }
@@ -209,6 +228,13 @@ void Context::emitBlockHeader(Codegen *codegen)
         }
     }
 
+    if (contextType == ContextType::Block && sizeOfRegisterTemporalDeadZone > 0) {
+        Instruction::InitializeBlockDeadTemporalZone tdzInit;
+        tdzInit.firstReg = registerOffset + nRegisters - sizeOfRegisterTemporalDeadZone;
+        tdzInit.count = sizeOfRegisterTemporalDeadZone;
+        bytecodeGenerator->addInstruction(tdzInit);
+    }
+
     if (usesThis) {
         Q_ASSERT(!isStrict);
         // make sure we convert this to an object
@@ -295,13 +321,23 @@ void Context::setupFunctionIndices(Moth::BytecodeGenerator *bytecodeGenerator)
     Q_ASSERT(nRegisters == 0);
     registerOffset = bytecodeGenerator->currentRegister();
 
-    if (contextType == ContextType::ESModule && !localNameForDefaultExport.isEmpty()) {
-        if (!members.contains(localNameForDefaultExport)) {
-            // allocate a local slot for the default export, to be used in
-            // CodeGen::visit(ExportDeclaration*).
-            locals.append(localNameForDefaultExport);
+    QVector<Context::MemberMap::Iterator> localsInTDZ;
+    const auto registerLocal = [this, &localsInTDZ](Context::MemberMap::iterator member) {
+        if (member->isLexicallyScoped()) {
+            localsInTDZ << member;
+        } else {
+            member->index = locals.size();
+            locals.append(member.key());
         }
-    }
+    };
+
+    QVector<Context::MemberMap::Iterator> registersInTDZ;
+    const auto allocateRegister = [bytecodeGenerator, &registersInTDZ](Context::MemberMap::iterator member) {
+        if (member->isLexicallyScoped())
+            registersInTDZ << member;
+        else
+            member->index = bytecodeGenerator->newRegister();
+    };
 
     switch (contextType) {
     case ContextType::ESModule:
@@ -309,15 +345,13 @@ void Context::setupFunctionIndices(Moth::BytecodeGenerator *bytecodeGenerator)
     case ContextType::Function:
     case ContextType::Binding: {
         for (Context::MemberMap::iterator it = members.begin(), end = members.end(); it != end; ++it) {
-            const QString &local = it.key();
             if (it->canEscape) {
-                it->index = locals.size();
-                locals.append(local);
+                registerLocal(it);
             } else {
                 if (it->type == Context::ThisFunctionName)
                     it->index = CallData::Function;
                 else
-                    it->index = bytecodeGenerator->newRegister();
+                    allocateRegister(it);
             }
         }
         break;
@@ -327,15 +361,34 @@ void Context::setupFunctionIndices(Moth::BytecodeGenerator *bytecodeGenerator)
         for (Context::MemberMap::iterator it = members.begin(), end = members.end(); it != end; ++it) {
             if (!it->isLexicallyScoped() && (contextType == ContextType::Global || !isStrict))
                 continue;
-            if (it->canEscape) {
-                it->index = locals.size();
-                locals.append(it.key());
-            } else {
-                it->index = bytecodeGenerator->newRegister();
-            }
+            if (it->canEscape)
+                registerLocal(it);
+            else
+                allocateRegister(it);
         }
         break;
     }
+
+    sizeOfLocalTemporalDeadZone = localsInTDZ.count();
+    for (auto &member: qAsConst(localsInTDZ)) {
+        member->index = locals.size();
+        locals.append(member.key());
+    }
+
+    if (contextType == ContextType::ESModule && !localNameForDefaultExport.isEmpty()) {
+        if (!members.contains(localNameForDefaultExport)) {
+            // allocate a local slot for the default export, to be used in
+            // CodeGen::visit(ExportDeclaration*).
+            locals.append(localNameForDefaultExport);
+            ++sizeOfLocalTemporalDeadZone;
+        }
+    }
+
+    sizeOfRegisterTemporalDeadZone = registersInTDZ.count();
+    firstTemporalDeadZoneRegister = bytecodeGenerator->currentRegister();
+    for (auto &member: qAsConst(registersInTDZ))
+        member->index = bytecodeGenerator->newRegister();
+
     nRegisters = bytecodeGenerator->currentRegister() - registerOffset;
 }
 
diff --git a/src/qml/compiler/qv4compilercontext_p.h b/src/qml/compiler/qv4compilercontext_p.h
index bd0bd90a59..3df0aa6b3a 100644
--- a/src/qml/compiler/qv4compilercontext_p.h
+++ b/src/qml/compiler/qv4compilercontext_p.h
@@ -167,8 +167,10 @@ struct Context {
         QQmlJS::AST::VariableScope scope = QQmlJS::AST::VariableScope::Var;
         mutable bool canEscape = false;
         QQmlJS::AST::FunctionExpression *function = nullptr;
+        QQmlJS::AST::SourceLocation endOfInitializerLocation;
 
         bool isLexicallyScoped() const { return this->scope != QQmlJS::AST::VariableScope::Var; }
+        bool requiresTDZCheck(const QQmlJS::AST::SourceLocation &accessLocation, bool accessAcrossContextBoundaries) const;
     };
     typedef QMap<QString, Member> MemberMap;
 
@@ -189,6 +191,9 @@ struct Context {
 
     int nRegisters = 0;
     int registerOffset = -1;
+    int sizeOfLocalTemporalDeadZone = 0;
+    int firstTemporalDeadZoneRegister = 0;
+    int sizeOfRegisterTemporalDeadZone = 0;
     bool hasDirectEval = false;
     bool allVarsEscape = false;
     bool hasNestedFunctions = false;
@@ -203,6 +208,7 @@ struct Context {
     bool isWithBlock = false;
     bool isCatchBlock = false;
     QString caughtVariable;
+    QQmlJS::AST::SourceLocation lastBlockInitializerLocation;
 
     enum UsesArgumentsObject {
         ArgumentsObjectUnknown,
@@ -310,7 +316,8 @@ struct Context {
         usedVariables.insert(name);
     }
 
-    bool addLocalVar(const QString &name, MemberType contextType, QQmlJS::AST::VariableScope scope, QQmlJS::AST::FunctionExpression *function = nullptr);
+    bool addLocalVar(const QString &name, MemberType contextType, QQmlJS::AST::VariableScope scope, QQmlJS::AST::FunctionExpression *function = nullptr,
+                     const QQmlJS::AST::SourceLocation &endOfInitializer = QQmlJS::AST::SourceLocation());
 
     struct ResolvedName {
         enum Type {
@@ -323,11 +330,13 @@ struct Context {
         Type type = Unresolved;
         bool isArgOrEval = false;
         bool isConst = false;
+        bool requiresTDZCheck = false;
         int scope = -1;
         int index = -1;
+        QQmlJS::AST::SourceLocation endOfDeclarationLocation;
         bool isValid() const { return type != Unresolved; }
     };
-    ResolvedName resolveName(const QString &name);
+    ResolvedName resolveName(const QString &name, const QQmlJS::AST::SourceLocation &accessLocation);
     void emitBlockHeader(Compiler::Codegen *codegen);
     void emitBlockFooter(Compiler::Codegen *codegen);
 
diff --git a/src/qml/compiler/qv4compilerscanfunctions.cpp b/src/qml/compiler/qv4compilerscanfunctions.cpp
index 06335b3aa0..5d3a7a6d8c 100644
--- a/src/qml/compiler/qv4compilerscanfunctions.cpp
+++ b/src/qml/compiler/qv4compilerscanfunctions.cpp
@@ -312,6 +312,10 @@ bool ScanFunctions::visit(PatternElement *ast)
     QStringList names;
     ast->boundNames(&names);
 
+    QQmlJS::AST::SourceLocation lastInitializerLocation = ast->lastSourceLocation();
+    if (_context->lastBlockInitializerLocation.isValid())
+        lastInitializerLocation = _context->lastBlockInitializerLocation;
+
     for (const QString &name : qAsConst(names)) {
         if (_context->isStrict && (name == QLatin1String("eval") || name == QLatin1String("arguments")))
             _cg->throwSyntaxError(ast->identifierToken, QStringLiteral("Variable name may not be eval or arguments in strict mode"));
@@ -322,7 +326,8 @@ bool ScanFunctions::visit(PatternElement *ast)
             _cg->throwSyntaxError(ast->identifierToken, QStringLiteral("Missing initializer in const declaration"));
             return false;
         }
-        if (!_context->addLocalVar(name, ast->initializer ? Context::VariableDefinition : Context::VariableDeclaration, ast->scope)) {
+        if (!_context->addLocalVar(name, ast->initializer ? Context::VariableDefinition : Context::VariableDeclaration, ast->scope,
+                                   /*function*/nullptr, lastInitializerLocation)) {
             _cg->throwSyntaxError(ast->identifierToken, QStringLiteral("Identifier %1 has already been declared").arg(name));
             return false;
         }
@@ -485,6 +490,8 @@ void ScanFunctions::endVisit(ForStatement *)
 
 bool ScanFunctions::visit(ForEachStatement *ast) {
     enterEnvironment(ast, ContextType::Block, QStringLiteral("%Foreach"));
+    if (ast->expression)
+        _context->lastBlockInitializerLocation = ast->expression->lastSourceLocation();
     Node::accept(ast->lhs, this);
     Node::accept(ast->expression, this);
 
diff --git a/src/qml/compiler/qv4instr_moth.cpp b/src/qml/compiler/qv4instr_moth.cpp
index d186c4e7e6..4653b7217d 100644
--- a/src/qml/compiler/qv4instr_moth.cpp
+++ b/src/qml/compiler/qv4instr_moth.cpp
@@ -156,7 +156,7 @@ QString dumpRegister(int reg, int nFormals)
         return QStringLiteral("(this)");
     else if (reg == CallData::Argc)
         return QStringLiteral("(argc)");
-    reg -= 4;
+    reg -= CallData::OffsetCount;
     if (reg <= nFormals)
         return QStringLiteral("a%1").arg(reg);
     reg -= nFormals;
@@ -415,6 +415,10 @@ void dumpBytecode(const char *code, int len, int nLocals, int nFormals, int /*st
                 d << "(" << level << ") " << ABSOLUTE_OFFSET();
         MOTH_END_INSTR(UnwindToLabel)
 
+        MOTH_BEGIN_INSTR(DeadTemporalZoneCheck)
+                d << name;
+        MOTH_END_INSTR(DeadTemporalZoneCheck)
+
         MOTH_BEGIN_INSTR(ThrowException)
         MOTH_END_INSTR(ThrowException)
 
@@ -690,6 +694,10 @@ void dumpBytecode(const char *code, int len, int nLocals, int nFormals, int /*st
         MOTH_BEGIN_INSTR(Debug)
         MOTH_END_INSTR(Debug)
 
+        MOTH_BEGIN_INSTR(InitializeBlockDeadTemporalZone)
+            d << dumpRegister(firstReg, nFormals) << ", " << count;
+        MOTH_END_INSTR(InitializeBlockDeadTemporalZone)
+
         MOTH_BEGIN_INSTR(LoadQmlContext)
             d << dumpRegister(result, nFormals);
         MOTH_END_INSTR(LoadQmlContext)
diff --git a/src/qml/compiler/qv4instr_moth_p.h b/src/qml/compiler/qv4instr_moth_p.h
index 25a07208c2..7c2cbf717e 100644
--- a/src/qml/compiler/qv4instr_moth_p.h
+++ b/src/qml/compiler/qv4instr_moth_p.h
@@ -118,6 +118,7 @@ QT_BEGIN_NAMESPACE
 #define INSTR_SetUnwindHandler(op) INSTRUCTION(op, SetUnwindHandler, 1, offset)
 #define INSTR_UnwindDispatch(op) INSTRUCTION(op, UnwindDispatch, 0)
 #define INSTR_UnwindToLabel(op) INSTRUCTION(op, UnwindToLabel, 2, level, offset)
+#define INSTR_DeadTemporalZoneCheck(op) INSTRUCTION(op, DeadTemporalZoneCheck, 1, name)
 #define INSTR_ThrowException(op) INSTRUCTION(op, ThrowException, 0)
 #define INSTR_GetException(op) INSTRUCTION(op, GetException, 0)
 #define INSTR_SetException(op) INSTRUCTION(op, SetException, 0)
@@ -192,6 +193,7 @@ QT_BEGIN_NAMESPACE
 #define INSTR_Sub(op) INSTRUCTION(op, Sub, 1, lhs)
 #define INSTR_LoadQmlContext(op) INSTRUCTION(op, LoadQmlContext, 1, result)
 #define INSTR_LoadQmlImportedScripts(op) INSTRUCTION(op, LoadQmlImportedScripts, 1, result)
+#define INSTR_InitializeBlockDeadTemporalZone(op) INSTRUCTION(op, InitializeBlockDeadTemporalZone, 2, firstReg, count)
 
 #define FOR_EACH_MOTH_INSTR_ALL(F) \
     F(Nop) \
@@ -295,6 +297,7 @@ QT_BEGIN_NAMESPACE
     F(SetUnwindHandler) \
     F(UnwindDispatch) \
     F(UnwindToLabel) \
+    F(DeadTemporalZoneCheck) \
     F(ThrowException) \
     F(GetException) \
     F(SetException) \
@@ -326,6 +329,7 @@ QT_BEGIN_NAMESPACE
     F(LoadSuperConstructor) \
     F(PushScriptContext) \
     F(PopScriptContext) \
+    F(InitializeBlockDeadTemporalZone) \
     F(Debug) \
 
 #define MOTH_NUM_INSTRUCTIONS() (static_cast<int>(Moth::Instr::Type::Debug_Wide) + 1)
diff --git a/src/qml/jit/qv4baselineassembler.cpp b/src/qml/jit/qv4baselineassembler.cpp
index c7d8f3c72c..5950901499 100644
--- a/src/qml/jit/qv4baselineassembler.cpp
+++ b/src/qml/jit/qv4baselineassembler.cpp
@@ -66,6 +66,7 @@ namespace JIT {
 #define callHelper(x) PlatformAssemblerCommon::callRuntimeUnchecked(#x, reinterpret_cast<void *>(&x))
 
 const QV4::Value::ValueTypeInternal IntegerTag = QV4::Value::ValueTypeInternal::Integer;
+const QV4::Value::ValueTypeInternal EmptyTag = QV4::Value::ValueTypeInternal::Empty;
 
 static ReturnedValue toNumberHelper(ReturnedValue v)
 {
@@ -172,6 +173,11 @@ public:
         return branch64(Equal, AccumulatorRegister, TrustedImm64(Primitive::emptyValue().asReturnedValue()));
     }
 
+    Jump jumpNotEmpty()
+    {
+        return branch64(NotEqual, AccumulatorRegister, TrustedImm64(Primitive::emptyValue().asReturnedValue()));
+    }
+
     void toBoolean(std::function<void(RegisterID)> continuation)
     {
         urshift64(AccumulatorRegister, TrustedImm32(Value::IsIntegerConvertible_Shift), ScratchRegister);
@@ -634,6 +640,11 @@ public:
         return branch32(Equal, AccumulatorRegisterTag, TrustedImm32(Primitive::emptyValue().asReturnedValue() >> 32));
     }
 
+    Jump jumpNotEmpty()
+    {
+        return branch32(NotEqual, AccumulatorRegisterTag, TrustedImm32(Primitive::emptyValue().asReturnedValue() >> 32));
+    }
+
     void toBoolean(std::function<void(RegisterID)> continuation)
     {
         urshift32(AccumulatorRegisterTag, TrustedImm32(Value::IsIntegerConvertible_Shift - 32),
@@ -1538,6 +1549,19 @@ void BaselineAssembler::popContext()
     pasm()->storeHeapObject(PlatformAssembler::ScratchRegister, regAddr(CallData::Context));
 }
 
+void BaselineAssembler::deadTemporalZoneCheck(int offsetForSavedIP, int variableName)
+{
+    auto valueIsAliveJump = pasm()->jumpNotEmpty();
+    storeInstructionPointer(offsetForSavedIP);
+    saveAccumulatorInFrame();
+    prepareCallWithArgCount(2);
+    passInt32AsArg(variableName, 1);
+    passEngineAsArg(0);
+    ASM_GENERATE_RUNTIME_CALL(Runtime::method_throwReferenceError, CallResultDestination::Ignore);
+    gotoCatchException();
+    valueIsAliveJump.link(pasm());
+}
+
 void BaselineAssembler::ret()
 {
     pasm()->generateFunctionExit();
diff --git a/src/qml/jit/qv4baselineassembler_p.h b/src/qml/jit/qv4baselineassembler_p.h
index 4b64f91cd4..a2140ce47b 100644
--- a/src/qml/jit/qv4baselineassembler_p.h
+++ b/src/qml/jit/qv4baselineassembler_p.h
@@ -161,6 +161,7 @@ public:
     void unwindToLabel(int level, int offset);
     void pushCatchContext(int index, int name);
     void popContext();
+    void deadTemporalZoneCheck(int offsetForSavedIP, int variableName);
 
     // other stuff
     void ret();
diff --git a/src/qml/jit/qv4baselinejit.cpp b/src/qml/jit/qv4baselinejit.cpp
index b729f21059..36375461f9 100644
--- a/src/qml/jit/qv4baselinejit.cpp
+++ b/src/qml/jit/qv4baselinejit.cpp
@@ -579,6 +579,10 @@ void BaselineJIT::generate_UnwindToLabel(int level, int offset)
     as->unwindToLabel(level, absoluteOffsetForJump(offset));
 }
 
+void BaselineJIT::generate_DeadTemporalZoneCheck(int name)
+{
+    as->deadTemporalZoneCheck(nextInstructionOffset(), name);
+}
 
 void BaselineJIT::generate_ThrowException()
 {
@@ -811,7 +815,7 @@ void BaselineJIT::generate_LoadSuperConstructor()
     as->prepareCallWithArgCount(2);
     as->passJSSlotAsArg(CallData::Function, 1);
     as->passEngineAsArg(0);
-    BASELINEJIT_GENERATE_RUNTIME_CALL(Helpers::loadSuperConstructor, CallResultDestination::InAccumulator);
+    BASELINEJIT_GENERATE_RUNTIME_CALL(Runtime::method_loadSuperConstructor, CallResultDestination::InAccumulator);
     as->checkException();
 }
 
@@ -931,6 +935,13 @@ void BaselineJIT::generate_LoadQmlImportedScripts(int result)
     as->storeReg(result);
 }
 
+void BaselineJIT::generate_InitializeBlockDeadTemporalZone(int firstReg, int count)
+{
+    as->loadValue(Primitive::emptyValue().rawValue());
+    for (int i = firstReg, end = firstReg + count; i < end; ++i)
+        as->storeReg(i);
+}
+
 void BaselineJIT::startInstruction(Instr::Type /*instr*/)
 {
     if (hasLabel())
diff --git a/src/qml/jit/qv4baselinejit_p.h b/src/qml/jit/qv4baselinejit_p.h
index 07a1853816..a3cb850fc1 100644
--- a/src/qml/jit/qv4baselinejit_p.h
+++ b/src/qml/jit/qv4baselinejit_p.h
@@ -134,6 +134,7 @@ public:
     void generate_SetUnwindHandler(int offset) override;
     void generate_UnwindDispatch() override;
     void generate_UnwindToLabel(int level, int offset) override;
+    void generate_DeadTemporalZoneCheck(int name) override;
     void generate_ThrowException() override;
     void generate_GetException() override;
     void generate_SetException() override;
@@ -208,6 +209,7 @@ public:
     void generate_Sub(int lhs) override;
     void generate_LoadQmlContext(int result) override;
     void generate_LoadQmlImportedScripts(int result) override;
+    void generate_InitializeBlockDeadTemporalZone(int firstReg, int count) override;
 
     void startInstruction(Moth::Instr::Type instr) override;
     void endInstruction(Moth::Instr::Type instr) override;
diff --git a/src/qml/jit/qv4jithelpers.cpp b/src/qml/jit/qv4jithelpers.cpp
index 9e057dd33d..7bac5d968d 100644
--- a/src/qml/jit/qv4jithelpers.cpp
+++ b/src/qml/jit/qv4jithelpers.cpp
@@ -70,16 +70,6 @@ ReturnedValue loadGlobalLookup(ExecutionEngine *engine, Function *f, int index)
     return l->globalGetter(l, engine);
 }
 
-ReturnedValue loadSuperConstructor(ExecutionEngine *engine, const Value *t)
-{
-    const FunctionObject *f = t->as<FunctionObject>();
-    if (!f || !f->isConstructor()) {
-        engine->throwTypeError();
-        return Encode::undefined();
-    }
-    return static_cast<const Object *>(t)->getPrototypeOf()->asReturnedValue();
-}
-
 ReturnedValue toObject(ExecutionEngine *engine, const Value &obj)
 {
     if (obj.isObject())
diff --git a/src/qml/jit/qv4jithelpers_p.h b/src/qml/jit/qv4jithelpers_p.h
index e0dfdc47d9..bb10d5722b 100644
--- a/src/qml/jit/qv4jithelpers_p.h
+++ b/src/qml/jit/qv4jithelpers_p.h
@@ -66,7 +66,6 @@ namespace Helpers {
 
 void convertThisToObject(ExecutionEngine *engine, Value *t);
 ReturnedValue loadGlobalLookup(ExecutionEngine *engine, Function *f, int index);
-ReturnedValue loadSuperConstructor(ExecutionEngine *engine, const Value *t);
 ReturnedValue toObject(ExecutionEngine *engine, const Value &obj);
 ReturnedValue exp(const Value &base, const Value &exp);
 ReturnedValue getLookup(ExecutionEngine *engine, Function *f, int index, const Value &base);
diff --git a/src/qml/jsruntime/qv4arrayobject.cpp b/src/qml/jsruntime/qv4arrayobject.cpp
index c162a38e9d..042d296276 100644
--- a/src/qml/jsruntime/qv4arrayobject.cpp
+++ b/src/qml/jsruntime/qv4arrayobject.cpp
@@ -49,6 +49,7 @@
 #include "qv4string_p.h"
 #include "qv4symbol_p.h"
 #include <QtCore/qscopedvaluerollback.h>
+#include "qv4proxy_p.h"
 
 using namespace QV4;
 
@@ -157,11 +158,12 @@ void ArrayPrototype::init(ExecutionEngine *engine, Object *ctor)
 
 ReturnedValue ArrayPrototype::method_isArray(const FunctionObject *, const Value *, const Value *argv, int argc)
 {
-    bool isArray = argc && argv[0].as<ArrayObject>();
-    return Encode(isArray);
+    if (!argc || !argv->objectValue())
+        return Encode(false);
+    return Encode(argv->objectValue()->isArray());
 }
 
-ScopedObject createObjectFromCtorOrArray(Scope &scope, ScopedFunctionObject ctor, bool useLen, int len)
+static ScopedObject createObjectFromCtorOrArray(Scope &scope, ScopedFunctionObject ctor, bool useLen, int len)
 {
     ScopedObject a(scope, Primitive::undefinedValue());
 
diff --git a/src/qml/jsruntime/qv4context.cpp b/src/qml/jsruntime/qv4context.cpp
index 327e7b78c4..d22179173c 100644
--- a/src/qml/jsruntime/qv4context.cpp
+++ b/src/qml/jsruntime/qv4context.cpp
@@ -76,6 +76,8 @@ Heap::CallContext *ExecutionContext::newBlockContext(CppStackFrame *frame, int b
     c->locals.size = nLocals;
     c->locals.alloc = nLocals;
 
+    c->setupLocalTemporalDeadZone(function->compilationUnit->unitData()->blockAt(blockIndex));
+
     return c;
 }
 
@@ -115,6 +117,8 @@ Heap::CallContext *ExecutionContext::newCallContext(CppStackFrame *frame)
     // memory allocated from the JS heap is 0 initialized, so check if empty is 0
     Q_ASSERT(Primitive::undefinedValue().asReturnedValue() == 0);
 
+    c->setupLocalTemporalDeadZone(compiledFunction);
+
     Value *args = c->locals.values + nLocals;
     ::memcpy(args, frame->originalArguments, frame->originalArgumentsCount * sizeof(Value));
     c->nArgs = frame->originalArgumentsCount;
diff --git a/src/qml/jsruntime/qv4context_p.h b/src/qml/jsruntime/qv4context_p.h
index fbb4168e9b..5de11d80cb 100644
--- a/src/qml/jsruntime/qv4context_p.h
+++ b/src/qml/jsruntime/qv4context_p.h
@@ -118,6 +118,12 @@ DECLARE_HEAP_OBJECT(CallContext, ExecutionContext) {
         return locals.data() + locals.size;
     }
     void setArg(uint index, Value v);
+
+    template <typename BlockOrFunction>
+    void setupLocalTemporalDeadZone(BlockOrFunction *bof) {
+        for (uint i = bof->nLocals - bof->sizeOfLocalTemporalDeadZone; i < bof->nLocals; ++i)
+            locals.values[i] = Primitive::emptyValue();
+    }
 };
 Q_STATIC_ASSERT(std::is_trivial< CallContext >::value);
 Q_STATIC_ASSERT(std::is_standard_layout<CallContextData>::value);
diff --git a/src/qml/jsruntime/qv4engine.cpp b/src/qml/jsruntime/qv4engine.cpp
index d6cfb1dcc1..c40d6414ff 100644
--- a/src/qml/jsruntime/qv4engine.cpp
+++ b/src/qml/jsruntime/qv4engine.cpp
@@ -485,10 +485,18 @@ ExecutionEngine::ExecutionEngine(QJSEngine *jsEngine)
     sequencePrototype()->cast<SequencePrototype>()->init();
 #endif
 
+    jsObjects[WeakMap_Ctor] = memoryManager->allocate<WeakMapCtor>(global);
+    jsObjects[WeakMapProto] = memoryManager->allocate<WeakMapPrototype>();
+    static_cast<WeakMapPrototype *>(weakMapPrototype())->init(this, weakMapCtor());
+
     jsObjects[Map_Ctor] = memoryManager->allocate<MapCtor>(global);
     jsObjects[MapProto] = memoryManager->allocate<MapPrototype>();
     static_cast<MapPrototype *>(mapPrototype())->init(this, mapCtor());
 
+    jsObjects[WeakSet_Ctor] = memoryManager->allocate<WeakSetCtor>(global);
+    jsObjects[WeakSetProto] = memoryManager->allocate<WeakSetPrototype>();
+    static_cast<WeakSetPrototype *>(weakSetPrototype())->init(this, weakSetCtor());
+
     jsObjects[Set_Ctor] = memoryManager->allocate<SetCtor>(global);
     jsObjects[SetProto] = memoryManager->allocate<SetPrototype>();
     static_cast<SetPrototype *>(setPrototype())->init(this, setCtor());
@@ -547,7 +555,9 @@ ExecutionEngine::ExecutionEngine(QJSEngine *jsEngine)
     globalObject->defineDefaultProperty(QStringLiteral("SharedArrayBuffer"), *sharedArrayBufferCtor());
     globalObject->defineDefaultProperty(QStringLiteral("ArrayBuffer"), *arrayBufferCtor());
     globalObject->defineDefaultProperty(QStringLiteral("DataView"), *dataViewCtor());
+    globalObject->defineDefaultProperty(QStringLiteral("WeakSet"), *weakSetCtor());
     globalObject->defineDefaultProperty(QStringLiteral("Set"), *setCtor());
+    globalObject->defineDefaultProperty(QStringLiteral("WeakMap"), *weakMapCtor());
     globalObject->defineDefaultProperty(QStringLiteral("Map"), *mapCtor());
 
     for (int i = 0; i < NTypedArrayTypes; ++i)
diff --git a/src/qml/jsruntime/qv4engine_p.h b/src/qml/jsruntime/qv4engine_p.h
index 0f4a4a75a2..0b5d8663eb 100644
--- a/src/qml/jsruntime/qv4engine_p.h
+++ b/src/qml/jsruntime/qv4engine_p.h
@@ -165,7 +165,9 @@ public:
         SharedArrayBufferProto,
         ArrayBufferProto,
         DataViewProto,
+        WeakSetProto,
         SetProto,
+        WeakMapProto,
         MapProto,
         IntrinsicTypedArrayProto,
         ValueTypeProto,
@@ -197,7 +199,9 @@ public:
         SharedArrayBuffer_Ctor,
         ArrayBuffer_Ctor,
         DataView_Ctor,
+        WeakSet_Ctor,
         Set_Ctor,
+        WeakMap_Ctor,
         Map_Ctor,
         IntrinsicTypedArray_Ctor,
 
@@ -234,7 +238,9 @@ public:
     FunctionObject *sharedArrayBufferCtor() const { return reinterpret_cast<FunctionObject *>(jsObjects + SharedArrayBuffer_Ctor); }
     FunctionObject *arrayBufferCtor() const { return reinterpret_cast<FunctionObject *>(jsObjects + ArrayBuffer_Ctor); }
     FunctionObject *dataViewCtor() const { return reinterpret_cast<FunctionObject *>(jsObjects + DataView_Ctor); }
+    FunctionObject *weakSetCtor() const { return reinterpret_cast<FunctionObject *>(jsObjects + WeakSet_Ctor); }
     FunctionObject *setCtor() const { return reinterpret_cast<FunctionObject *>(jsObjects + Set_Ctor); }
+    FunctionObject *weakMapCtor() const { return reinterpret_cast<FunctionObject *>(jsObjects + WeakMap_Ctor); }
     FunctionObject *mapCtor() const { return reinterpret_cast<FunctionObject *>(jsObjects + Map_Ctor); }
     FunctionObject *intrinsicTypedArrayCtor() const { return reinterpret_cast<FunctionObject *>(jsObjects + IntrinsicTypedArray_Ctor); }
     FunctionObject *typedArrayCtors;
@@ -268,7 +274,9 @@ public:
     Object *sharedArrayBufferPrototype() const { return reinterpret_cast<Object *>(jsObjects + SharedArrayBufferProto); }
     Object *arrayBufferPrototype() const { return reinterpret_cast<Object *>(jsObjects + ArrayBufferProto); }
     Object *dataViewPrototype() const { return reinterpret_cast<Object *>(jsObjects + DataViewProto); }
+    Object *weakSetPrototype() const { return reinterpret_cast<Object *>(jsObjects + WeakSetProto); }
     Object *setPrototype() const { return reinterpret_cast<Object *>(jsObjects + SetProto); }
+    Object *weakMapPrototype() const { return reinterpret_cast<Object *>(jsObjects + WeakMapProto); }
     Object *mapPrototype() const { return reinterpret_cast<Object *>(jsObjects + MapProto); }
     Object *intrinsicTypedArrayPrototype() const { return reinterpret_cast<Object *>(jsObjects + IntrinsicTypedArrayProto); }
     Object *typedArrayPrototype;
diff --git a/src/qml/jsruntime/qv4estable.cpp b/src/qml/jsruntime/qv4estable.cpp
index 55b7407000..aa39971dc6 100644
--- a/src/qml/jsruntime/qv4estable.cpp
+++ b/src/qml/jsruntime/qv4estable.cpp
@@ -38,6 +38,7 @@
 ****************************************************************************/
 
 #include "qv4estable_p.h"
+#include "qv4object_p.h"
 
 using namespace QV4;
 
@@ -67,10 +68,11 @@ ESTable::~ESTable()
     m_values = nullptr;
 }
 
-void ESTable::markObjects(MarkStack *s)
+void ESTable::markObjects(MarkStack *s, bool isWeakMap)
 {
     for (uint i = 0; i < m_size; ++i) {
-        m_keys[i].mark(s);
+        if (!isWeakMap)
+            m_keys[i].mark(s);
         m_values[i].mark(s);
     }
 }
@@ -155,8 +157,8 @@ bool ESTable::remove(const Value &key)
     }
 
     if (found == true) {
-        memmove(m_keys + idx, m_keys + idx + 1, m_size - idx);
-        memmove(m_values + idx, m_values + idx + 1, m_size - idx);
+        memmove(m_keys + idx, m_keys + idx + 1, (m_size - idx)*sizeof(Value));
+        memmove(m_values + idx, m_values + idx + 1, (m_size - idx)*sizeof(Value));
         m_size--;
     }
     return found;
@@ -179,3 +181,19 @@ void ESTable::iterate(uint idx, Value *key, Value *value)
     *value = m_values[idx];
 }
 
+void ESTable::removeUnmarkedKeys()
+{
+    uint idx = 0;
+    uint toIdx = 0;
+    for (; idx < m_size; ++idx) {
+        Q_ASSERT(m_keys[idx].isObject());
+        Object &o = static_cast<Object &>(m_keys[idx]);
+        if (o.d()->isMarked()) {
+            m_keys[toIdx] = m_keys[idx];
+            m_values[toIdx] = m_values[idx];
+            ++toIdx;
+        }
+    }
+    m_size = toIdx;
+}
+
diff --git a/src/qml/jsruntime/qv4estable_p.h b/src/qml/jsruntime/qv4estable_p.h
index c665467760..f54fc37a7b 100644
--- a/src/qml/jsruntime/qv4estable_p.h
+++ b/src/qml/jsruntime/qv4estable_p.h
@@ -64,7 +64,7 @@ public:
     ESTable();
     ~ESTable();
 
-    void markObjects(MarkStack *s);
+    void markObjects(MarkStack *s, bool isWeakMap);
     void clear();
     void set(const Value &k, const Value &v);
     bool has(const Value &k) const;
@@ -73,6 +73,8 @@ public:
     uint size() const;
     void iterate(uint idx, Value *k, Value *v);
 
+    void removeUnmarkedKeys();
+
 private:
     Value *m_keys = nullptr;
     Value *m_values = nullptr;
diff --git a/src/qml/jsruntime/qv4functionobject.cpp b/src/qml/jsruntime/qv4functionobject.cpp
index a5dc0ba567..f7bea9a5f0 100644
--- a/src/qml/jsruntime/qv4functionobject.cpp
+++ b/src/qml/jsruntime/qv4functionobject.cpp
@@ -556,7 +556,7 @@ ReturnedValue ConstructorFunction::virtualCallAsConstructor(const FunctionObject
     CppStackFrame frame;
     frame.init(v4, f->function(), argv, argc);
     frame.setupJSFrame(v4->jsStackTop, *f, f->scope(),
-                       Primitive::undefinedValue(),
+                       Primitive::emptyValue(),
                        newTarget ? *newTarget : Primitive::undefinedValue());
 
     frame.push();
@@ -570,7 +570,7 @@ ReturnedValue ConstructorFunction::virtualCallAsConstructor(const FunctionObject
         return Encode::undefined();
     else if (Value::fromReturnedValue(result).isObject())
         return result;
-    else if (!Value::fromReturnedValue(result).isUndefined())
+    else if (!Value::fromReturnedValue(result).isUndefined() || frame.jsFrame->thisObject.isEmpty())
         return v4->throwTypeError();
     return frame.jsFrame->thisObject.asReturnedValue();
 }
diff --git a/src/qml/jsruntime/qv4global_p.h b/src/qml/jsruntime/qv4global_p.h
index e812894a97..f89a4b9909 100644
--- a/src/qml/jsruntime/qv4global_p.h
+++ b/src/qml/jsruntime/qv4global_p.h
@@ -195,6 +195,9 @@ namespace Heap {
     struct DataView;
     struct TypedArray;
 
+    struct MapObject;
+    struct SetObject;
+
     template <typename T, size_t> struct Pointer;
 }
 
@@ -242,6 +245,9 @@ struct ArrayBuffer;
 struct DataView;
 struct TypedArray;
 
+struct MapObject;
+struct SetMapObject;
+
 // ReturnedValue is used to return values from runtime methods
 // the type has to be a primitive type (no struct or union), so that the compiler
 // will return it in a register on all platforms.
diff --git a/src/qml/jsruntime/qv4jscall_p.h b/src/qml/jsruntime/qv4jscall_p.h
index 55cedf50aa..31689b1ba1 100644
--- a/src/qml/jsruntime/qv4jscall_p.h
+++ b/src/qml/jsruntime/qv4jscall_p.h
@@ -86,6 +86,7 @@ struct JSCallData {
         ptr->context = Encode::undefined();
         ptr->accumulator = Encode::undefined();
         ptr->thisObject = thisObject->asReturnedValue();
+        ptr->newTarget = Encode::undefined();
         ptr->setArgc(argc);
         if (argc)
             memcpy(ptr->args, args, argc*sizeof(Value));
diff --git a/src/qml/jsruntime/qv4mapobject.cpp b/src/qml/jsruntime/qv4mapobject.cpp
index ca9e1723f9..c598814fb6 100644
--- a/src/qml/jsruntime/qv4mapobject.cpp
+++ b/src/qml/jsruntime/qv4mapobject.cpp
@@ -45,65 +45,112 @@
 
 using namespace QV4;
 
+DEFINE_OBJECT_VTABLE(WeakMapCtor);
 DEFINE_OBJECT_VTABLE(MapCtor);
 DEFINE_OBJECT_VTABLE(MapObject);
 
+void Heap::WeakMapCtor::init(QV4::ExecutionContext *scope)
+{
+    Heap::FunctionObject::init(scope, QStringLiteral("WeakMap"));
+}
+
 void Heap::MapCtor::init(QV4::ExecutionContext *scope)
 {
     Heap::FunctionObject::init(scope, QStringLiteral("Map"));
 }
 
-ReturnedValue MapCtor::virtualCallAsConstructor(const FunctionObject *f, const Value *argv, int argc, const Value *)
+ReturnedValue WeakMapCtor::construct(const FunctionObject *f, const Value *argv, int argc, const Value *, bool weakMap)
 {
     Scope scope(f);
     Scoped<MapObject> a(scope, scope.engine->memoryManager->allocate<MapObject>());
+    if (weakMap) {
+        a->setPrototypeOf(scope.engine->weakMapPrototype());
+        scope.engine->memoryManager->registerWeakMap(a->d());
+    }
+    a->d()->isWeakMap = weakMap;
 
     if (argc > 0) {
         ScopedValue iterable(scope, argv[0]);
 
-        // ### beware, hack alert!
-        // Object iteration seems broken right now. if we allow any object to
-        // iterate, it endlessly loops in the Map/prototype tests in test262...
-        // disable these for now until Object iteration is fixed, just so we can
-        // test this.
-        Scoped<MapObject> mapObjectCheck(scope, argv[0]);
-        Scoped<SetObject> setObjectCheck(scope, argv[0]);
-
-        if (!iterable->isUndefined() && !iterable->isNull() && (mapObjectCheck || setObjectCheck)) {
+        if (!iterable->isNullOrUndefined()) {
             ScopedFunctionObject adder(scope, a->get(ScopedString(scope, scope.engine->newString(QString::fromLatin1("set")))));
             if (!adder)
                 return scope.engine->throwTypeError();
-            ScopedObject iter(scope, Runtime::method_getIterator(scope.engine, iterable, true));
 
-            CHECK_EXCEPTION();
-            if (!iter)
-                return a.asReturnedValue();
+            ScopedObject iter(scope, Runtime::method_getIterator(scope.engine, iterable, true));
+            if (scope.hasException())
+                return Encode::undefined();
+            Q_ASSERT(iter);
 
-            Value *nextValue = scope.alloc(1);
+            ScopedValue obj(scope);
+            Value *arguments = scope.alloc(2);
             ScopedValue done(scope);
             forever {
-                done = Runtime::method_iteratorNext(scope.engine, iter, nextValue);
-                CHECK_EXCEPTION();
+                done = Runtime::method_iteratorNext(scope.engine, iter, obj);
+                if (scope.hasException())
+                    break;
                 if (done->toBoolean())
-                    return a.asReturnedValue();
-
-                adder->call(a, nextValue, 1);
-                if (scope.engine->hasException) {
-                    ScopedValue falsey(scope, Encode(false));
-                    return Runtime::method_iteratorClose(scope.engine, iter, falsey);
+                    return a->asReturnedValue();
+                const Object *o = obj->objectValue();
+                if (!o) {
+                    scope.engine->throwTypeError();
+                    break;
                 }
+
+                arguments[0] = o->get(PropertyKey::fromArrayIndex(0));
+                if (scope.hasException())
+                    break;
+                arguments[1] = o->get(PropertyKey::fromArrayIndex(1));
+                if (scope.hasException())
+                    break;
+
+                adder->call(a, arguments, 2);
+                if (scope.hasException())
+                    break;
             }
+            ScopedValue falsey(scope, Encode(false));
+            return Runtime::method_iteratorClose(scope.engine, iter, falsey);
         }
     }
-    return a.asReturnedValue();
+    return a->asReturnedValue();
+
 }
 
-ReturnedValue MapCtor::virtualCall(const FunctionObject *f, const Value *, const Value *, int)
+ReturnedValue WeakMapCtor::virtualCallAsConstructor(const FunctionObject *f, const Value *argv, int argc, const Value *newTarget)
+{
+    return construct(f, argv, argc, newTarget, true);
+}
+
+ReturnedValue WeakMapCtor::virtualCall(const FunctionObject *f, const Value *, const Value *, int)
 {
     Scope scope(f);
-    return scope.engine->throwTypeError(QString::fromLatin1("Map requires new"));
+    return scope.engine->throwTypeError(QString::fromLatin1("(Weak)Map requires new"));
+}
+
+
+ReturnedValue MapCtor::virtualCallAsConstructor(const FunctionObject *f, const Value *argv, int argc, const Value *newTarget)
+{
+    return construct(f, argv, argc, newTarget, false);
+}
+
+void WeakMapPrototype::init(ExecutionEngine *engine, Object *ctor)
+{
+    Scope scope(engine);
+    ScopedObject o(scope);
+    ctor->defineReadonlyConfigurableProperty(engine->id_length(), Primitive::fromInt32(0));
+    ctor->defineReadonlyProperty(engine->id_prototype(), (o = this));
+    defineDefaultProperty(engine->id_constructor(), (o = ctor));
+
+    defineDefaultProperty(QStringLiteral("delete"), method_delete, 1);
+    defineDefaultProperty(QStringLiteral("get"), method_get, 1);
+    defineDefaultProperty(QStringLiteral("has"), method_has, 1);
+    defineDefaultProperty(QStringLiteral("set"), method_set, 2);
+
+    ScopedString val(scope, engine->newString(QLatin1String("WeakMap")));
+    defineReadonlyConfigurableProperty(engine->symbol_toStringTag(), val);
 }
 
+
 void MapPrototype::init(ExecutionEngine *engine, Object *ctor)
 {
     Scope scope(engine);
@@ -119,7 +166,7 @@ void MapPrototype::init(ExecutionEngine *engine, Object *ctor)
     defineDefaultProperty(QStringLiteral("get"), method_get, 1);
     defineDefaultProperty(QStringLiteral("has"), method_has, 1);
     defineDefaultProperty(QStringLiteral("keys"), method_keys, 0);
-    defineDefaultProperty(QStringLiteral("set"), method_set, 0);
+    defineDefaultProperty(QStringLiteral("set"), method_set, 2);
     defineAccessorProperty(QStringLiteral("size"), method_get_size, nullptr);
     defineDefaultProperty(QStringLiteral("values"), method_values, 0);
 
@@ -142,42 +189,97 @@ void Heap::MapObject::init()
 void Heap::MapObject::destroy()
 {
     delete esTable;
-    esTable = 0;
+    esTable = nullptr;
+}
+
+void Heap::MapObject::removeUnmarkedKeys()
+{
+    esTable->removeUnmarkedKeys();
 }
 
 void Heap::MapObject::markObjects(Heap::Base *that, MarkStack *markStack)
 {
     MapObject *m = static_cast<MapObject *>(that);
-    m->esTable->markObjects(markStack);
+    m->esTable->markObjects(markStack, m->isWeakMap);
     Object::markObjects(that, markStack);
 }
 
+ReturnedValue WeakMapPrototype::method_delete(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
+{
+    Scope scope(b);
+    Scoped<MapObject> that(scope, thisObject);
+    if (!that || !that->d()->isWeakMap)
+        return scope.engine->throwTypeError();
+    if (!argc || !argv[0].isObject())
+        return Encode(false);
+
+    return Encode(that->d()->esTable->remove(argv[0]));
+
+}
+
+ReturnedValue WeakMapPrototype::method_get(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
+{
+    Scope scope(b);
+    Scoped<MapObject> that(scope, thisObject);
+    if (!that || !that->d()->isWeakMap)
+        return scope.engine->throwTypeError();
+    if (!argc || !argv[0].isObject())
+        return Encode::undefined();
+
+    return that->d()->esTable->get(argv[0]);
+}
+
+ReturnedValue WeakMapPrototype::method_has(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
+{
+    Scope scope(b);
+    Scoped<MapObject> that(scope, thisObject);
+    if (!that || !that->d()->isWeakMap)
+        return scope.engine->throwTypeError();
+    if (!argc || !argv[0].isObject())
+        return Encode(false);
+
+    return Encode(that->d()->esTable->has(argv[0]));
+}
+
+ReturnedValue WeakMapPrototype::method_set(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
+{
+    Scope scope(b);
+    Scoped<MapObject> that(scope, thisObject);
+    if ((!that || !that->d()->isWeakMap) ||
+        (!argc || !argv[0].isObject()))
+        return scope.engine->throwTypeError();
+
+    that->d()->esTable->set(argv[0], argc > 1 ? argv[1] : Primitive::undefinedValue());
+    return that.asReturnedValue();
+}
+
+
 ReturnedValue MapPrototype::method_clear(const FunctionObject *b, const Value *thisObject, const Value *, int)
 {
     Scope scope(b);
     Scoped<MapObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakMap)
         return scope.engine->throwTypeError();
 
     that->d()->esTable->clear();
     return Encode::undefined();
 }
 
-ReturnedValue MapPrototype::method_delete(const FunctionObject *b, const Value *thisObject, const Value *argv, int)
+ReturnedValue MapPrototype::method_delete(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
 {
     Scope scope(b);
     Scoped<MapObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakMap)
         return scope.engine->throwTypeError();
 
-    return Encode(that->d()->esTable->remove(argv[0]));
+    return Encode(that->d()->esTable->remove(argc ? argv[0] : Primitive::undefinedValue()));
 }
 
 ReturnedValue MapPrototype::method_entries(const FunctionObject *b, const Value *thisObject, const Value *, int)
 {
     Scope scope(b);
     Scoped<MapObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakMap)
         return scope.engine->throwTypeError();
 
     Scoped<MapIteratorObject> ao(scope, scope.engine->newMapIteratorObject(that));
@@ -189,7 +291,7 @@ ReturnedValue MapPrototype::method_forEach(const FunctionObject *b, const Value
 {
     Scope scope(b);
     Scoped<MapObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakMap)
         return scope.engine->throwTypeError();
 
     ScopedFunctionObject callbackfn(scope, argv[0]);
@@ -201,41 +303,41 @@ ReturnedValue MapPrototype::method_forEach(const FunctionObject *b, const Value
         thisArg = ScopedValue(scope, argv[1]);
 
     Value *arguments = scope.alloc(3);
+    arguments[2] = that;
     for (uint i = 0; i < that->d()->esTable->size(); ++i) {
-        that->d()->esTable->iterate(i, &arguments[0], &arguments[1]); // fill in key (0), value (1)
+        that->d()->esTable->iterate(i, &arguments[1], &arguments[0]); // fill in key (0), value (1)
 
-        arguments[2] = that;
         callbackfn->call(thisArg, arguments, 3);
         CHECK_EXCEPTION();
     }
     return Encode::undefined();
 }
 
-ReturnedValue MapPrototype::method_get(const FunctionObject *b, const Value *thisObject, const Value *argv, int)
+ReturnedValue MapPrototype::method_get(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
 {
     Scope scope(b);
     Scoped<MapObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakMap)
         return scope.engine->throwTypeError();
 
-    return that->d()->esTable->get(argv[0]);
+    return that->d()->esTable->get(argc ? argv[0] : Primitive::undefinedValue());
 }
 
-ReturnedValue MapPrototype::method_has(const FunctionObject *b, const Value *thisObject, const Value *argv, int)
+ReturnedValue MapPrototype::method_has(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
 {
     Scope scope(b);
     Scoped<MapObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakMap)
         return scope.engine->throwTypeError();
 
-    return Encode(that->d()->esTable->has(argv[0]));
+    return Encode(that->d()->esTable->has(argc ? argv[0] : Primitive::undefinedValue()));
 }
 
 ReturnedValue MapPrototype::method_keys(const FunctionObject *b, const Value *thisObject, const Value *, int)
 {
     Scope scope(b);
     Scoped<MapObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakMap)
         return scope.engine->throwTypeError();
 
     Scoped<MapIteratorObject> ao(scope, scope.engine->newMapIteratorObject(that));
@@ -243,14 +345,14 @@ ReturnedValue MapPrototype::method_keys(const FunctionObject *b, const Value *th
     return ao->asReturnedValue();
 }
 
-ReturnedValue MapPrototype::method_set(const FunctionObject *b, const Value *thisObject, const Value *argv, int)
+ReturnedValue MapPrototype::method_set(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
 {
     Scope scope(b);
     Scoped<MapObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakMap)
         return scope.engine->throwTypeError();
 
-    that->d()->esTable->set(argv[0], argv[1]);
+    that->d()->esTable->set(argc ? argv[0] : Primitive::undefinedValue(), argc > 1 ? argv[1] : Primitive::undefinedValue());
     return that.asReturnedValue();
 }
 
@@ -258,7 +360,7 @@ ReturnedValue MapPrototype::method_get_size(const FunctionObject *b, const Value
 {
     Scope scope(b);
     Scoped<MapObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakMap)
         return scope.engine->throwTypeError();
 
     return Encode(that->d()->esTable->size());
@@ -268,12 +370,10 @@ ReturnedValue MapPrototype::method_values(const FunctionObject *b, const Value *
 {
     Scope scope(b);
     Scoped<MapObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakMap)
         return scope.engine->throwTypeError();
 
     Scoped<MapIteratorObject> ao(scope, scope.engine->newMapIteratorObject(that));
     ao->d()->iterationKind = IteratorKind::ValueIteratorKind;
     return ao->asReturnedValue();
 }
-
-
diff --git a/src/qml/jsruntime/qv4mapobject_p.h b/src/qml/jsruntime/qv4mapobject_p.h
index 6793612bcb..a0fae2a14a 100644
--- a/src/qml/jsruntime/qv4mapobject_p.h
+++ b/src/qml/jsruntime/qv4mapobject_p.h
@@ -64,7 +64,11 @@ class ESTable;
 
 namespace Heap {
 
-struct MapCtor : FunctionObject {
+struct WeakMapCtor : FunctionObject {
+    void init(QV4::ExecutionContext *scope);
+};
+
+struct MapCtor : WeakMapCtor {
     void init(QV4::ExecutionContext *scope);
 };
 
@@ -72,19 +76,32 @@ struct MapObject : Object {
     static void markObjects(Heap::Base *that, MarkStack *markStack);
     void init();
     void destroy();
+    void removeUnmarkedKeys();
+
+    MapObject *nextWeakMap;
     ESTable *esTable;
+    bool isWeakMap;
 };
 
 }
 
-struct MapCtor: FunctionObject
+struct WeakMapCtor: FunctionObject
 {
-    V4_OBJECT2(MapCtor, FunctionObject)
+    V4_OBJECT2(WeakMapCtor, FunctionObject)
+
+    static ReturnedValue construct(const FunctionObject *f, const Value *argv, int argc, const Value *, bool weakMap);
 
     static ReturnedValue virtualCallAsConstructor(const FunctionObject *f, const Value *argv, int argc, const Value *);
     static ReturnedValue virtualCall(const FunctionObject *f, const Value *thisObject, const Value *argv, int argc);
 };
 
+struct MapCtor : WeakMapCtor
+{
+    V4_OBJECT2(MapCtor, WeakMapCtor)
+
+    static ReturnedValue virtualCallAsConstructor(const FunctionObject *f, const Value *argv, int argc, const Value *);
+};
+
 struct MapObject : Object
 {
     V4_OBJECT2(MapObject, Object)
@@ -92,7 +109,17 @@ struct MapObject : Object
     V4_NEEDS_DESTROY
 };
 
-struct MapPrototype : Object
+struct WeakMapPrototype : Object
+{
+    void init(ExecutionEngine *engine, Object *ctor);
+
+    static ReturnedValue method_delete(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
+    static ReturnedValue method_get(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
+    static ReturnedValue method_has(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
+    static ReturnedValue method_set(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
+};
+
+struct MapPrototype : WeakMapPrototype
 {
     void init(ExecutionEngine *engine, Object *ctor);
 
diff --git a/src/qml/jsruntime/qv4module.cpp b/src/qml/jsruntime/qv4module.cpp
index 583d0c3756..2db229e2b0 100644
--- a/src/qml/jsruntime/qv4module.cpp
+++ b/src/qml/jsruntime/qv4module.cpp
@@ -70,6 +70,9 @@ void Heap::Module::init(ExecutionEngine *engine, CompiledData::CompilationUnit *
     scope->locals.alloc = locals;
     scope->nArgs = 0;
 
+    // Prepare the temporal dead zone
+    scope->setupLocalTemporalDeadZone(moduleFunction->compiledFunction);
+
     Scope valueScope(engine);
 
     // It's possible for example to re-export an import, for example:
@@ -108,6 +111,10 @@ ReturnedValue Module::virtualGet(const Managed *m, PropertyKey id, const Value *
         *hasProperty = v != nullptr;
     if (!v)
         return Encode::undefined();
+    if (v->isEmpty()) {
+        ScopedValue propName(scope, id.toStringOrSymbol(scope.engine));
+        return scope.engine->throwReferenceError(propName);
+    }
     return v->asReturnedValue();
 }
 
@@ -126,10 +133,26 @@ PropertyAttributes Module::virtualGetOwnProperty(Managed *m, PropertyKey id, Pro
         return Attr_Invalid;
     }
     if (p)
-        p->value = v->asReturnedValue();
+        p->value = v->isEmpty() ? Encode::undefined() : v->asReturnedValue();
+    if (v->isEmpty()) {
+        ScopedValue propName(scope, id.toStringOrSymbol(scope.engine));
+        scope.engine->throwReferenceError(propName);
+    }
     return Attr_Data | Attr_NotConfigurable;
 }
 
+bool Module::virtualHasProperty(const Managed *m, PropertyKey id)
+{
+    if (id.isSymbol())
+        return Object::virtualHasProperty(m, id);
+
+    const Module *module = static_cast<const Module *>(m);
+    Scope scope(m->engine());
+    ScopedString expectedName(scope, id.toStringOrSymbol(scope.engine));
+    const Value *v = module->d()->unit->resolveExport(expectedName);
+    return v != nullptr;
+}
+
 bool Module::virtualPreventExtensions(Managed *)
 {
     return true;
@@ -179,8 +202,13 @@ PropertyKey ModuleNamespaceIterator::next(const Object *o, Property *pd, Propert
         Scope scope(module->engine());
         ScopedString exportName(scope, scope.engine->newString(exportedNames.at(exportIndex)));
         exportIndex++;
-        if (pd)
-            pd->value = *module->d()->unit->resolveExport(exportName);
+        const Value *v = module->d()->unit->resolveExport(exportName);
+        if (pd) {
+            if (v->isEmpty())
+                scope.engine->throwReferenceError(exportName);
+            else
+                pd->value = *v;
+        }
         return exportName->toPropertyKey();
     }
     return ObjectOwnPropertyKeyIterator::next(o, pd, attrs);
diff --git a/src/qml/jsruntime/qv4module_p.h b/src/qml/jsruntime/qv4module_p.h
index bb004b3b44..073e0d1e54 100644
--- a/src/qml/jsruntime/qv4module_p.h
+++ b/src/qml/jsruntime/qv4module_p.h
@@ -77,6 +77,7 @@ struct Q_QML_EXPORT Module : public Object {
 
     static ReturnedValue virtualGet(const Managed *m, PropertyKey id, const Value *receiver, bool *hasProperty);
     static PropertyAttributes virtualGetOwnProperty(Managed *m, PropertyKey id, Property *p);
+    static bool virtualHasProperty(const Managed *m, PropertyKey id);
     static bool virtualPreventExtensions(Managed *);
     static bool virtualDefineOwnProperty(Managed *, PropertyKey, const Property *, PropertyAttributes);
     static bool virtualPut(Managed *, PropertyKey, const Value &, Value *);
diff --git a/src/qml/jsruntime/qv4objectiterator.cpp b/src/qml/jsruntime/qv4objectiterator.cpp
index 3d193455e9..8158d8ddd9 100644
--- a/src/qml/jsruntime/qv4objectiterator.cpp
+++ b/src/qml/jsruntime/qv4objectiterator.cpp
@@ -115,8 +115,7 @@ ReturnedValue ObjectIterator::nextPropertyNameAsString()
 
     PropertyAttributes attrs;
     Scope scope(engine);
-    ScopedProperty p(scope);
-    ScopedPropertyKey key(scope, next(p, &attrs));
+    ScopedPropertyKey key(scope, next(nullptr, &attrs));
     if (!key->isValid())
         return Encode::null();
 
@@ -163,12 +162,13 @@ PropertyKey ForInIteratorObject::nextProperty() const
     Scope scope(this);
     ScopedObject c(scope, d()->current);
     ScopedObject o(scope);
+    ScopedProperty p(scope);
     ScopedPropertyKey key(scope);
     PropertyAttributes attrs;
 
     while (1) {
         while (1) {
-            key = d()->iterator->next(c, nullptr, &attrs);
+            key = d()->iterator->next(c, p, &attrs);
             if (!key->isValid())
                 break;
             if (!attrs.isEnumerable() || key->isSymbol())
diff --git a/src/qml/jsruntime/qv4objectproto.cpp b/src/qml/jsruntime/qv4objectproto.cpp
index c968bff0fe..926d246373 100644
--- a/src/qml/jsruntime/qv4objectproto.cpp
+++ b/src/qml/jsruntime/qv4objectproto.cpp
@@ -563,8 +563,9 @@ ReturnedValue ObjectPrototype::method_keys(const FunctionObject *b, const Value
 
     ObjectIterator it(scope, o, ObjectIterator::EnumerableOnly);
     ScopedValue name(scope);
+    ScopedValue value(scope);
     while (1) {
-        name = it.nextPropertyNameAsString();
+        name = it.nextPropertyNameAsString(value);
         if (name->isNull())
             break;
         a->push_back(name);
diff --git a/src/qml/jsruntime/qv4reflect.cpp b/src/qml/jsruntime/qv4reflect.cpp
index 3dc0956e0c..766a0c4592 100644
--- a/src/qml/jsruntime/qv4reflect.cpp
+++ b/src/qml/jsruntime/qv4reflect.cpp
@@ -200,9 +200,7 @@ ReturnedValue Reflect::method_has(const FunctionObject *f, const Value *, const
     if (scope.engine->hasException)
         return false;
 
-    bool hasProperty = false;
-    (void) o->get(name, nullptr, &hasProperty);
-    return Encode(hasProperty);
+    return Encode(o->hasProperty(name));
 }
 
 ReturnedValue Reflect::method_isExtensible(const FunctionObject *f, const Value *, const Value *argv, int argc)
diff --git a/src/qml/jsruntime/qv4runtime.cpp b/src/qml/jsruntime/qv4runtime.cpp
index 9180108a0c..3317003ea4 100644
--- a/src/qml/jsruntime/qv4runtime.cpp
+++ b/src/qml/jsruntime/qv4runtime.cpp
@@ -759,11 +759,15 @@ ReturnedValue Runtime::method_iteratorNext(ExecutionEngine *engine, const Value
     if (!o)
         return engine->throwTypeError();
     ScopedValue d(scope, o->get(engine->id_done()));
+    if (scope.hasException())
+        return Encode::undefined();
     bool done = d->toBoolean();
     if (done) {
         *value = Encode::undefined();
     } else {
         *value = o->get(engine->id_value());
+        if (scope.hasException())
+            return Encode::undefined();
     }
     return Encode(done);
 }
@@ -907,6 +911,22 @@ void Runtime::method_storeSuperProperty(ExecutionEngine *engine, const Value &pr
         engine->throwTypeError();
 }
 
+ReturnedValue Runtime::method_loadSuperConstructor(ExecutionEngine *engine, const Value &t)
+{
+    if (engine->currentStackFrame->thisObject() != Primitive::emptyValue().asReturnedValue()) {
+        return engine->throwReferenceError(QStringLiteral("super() already called."), QString(), 0, 0); // ### fix line number
+    }
+    const FunctionObject *f = t.as<FunctionObject>();
+    if (!f)
+        return engine->throwTypeError();
+    Heap::Object *c = static_cast<const Object &>(t).getPrototypeOf();
+    if (!c->vtable()->isFunctionObject || !static_cast<Heap::FunctionObject *>(c)->isConstructor())
+        return engine->throwTypeError();
+    return c->asReturnedValue();
+}
+
+
+
 #endif // V4_BOOTSTRAP
 
 uint RuntimeHelpers::equalHelper(const Value &x, const Value &y)
@@ -1364,7 +1384,6 @@ ReturnedValue Runtime::method_construct(ExecutionEngine *engine, const Value &fu
 
 ReturnedValue Runtime::method_constructWithSpread(ExecutionEngine *engine, const Value &function, const Value &newTarget, Value *argv, int argc)
 {
-    Q_UNIMPLEMENTED();
     if (!function.isFunctionObject())
         return engine->throwTypeError();
 
@@ -1470,6 +1489,12 @@ ReturnedValue Runtime::method_popScriptContext(ExecutionEngine *engine)
     return root;
 }
 
+void Runtime::method_throwReferenceError(ExecutionEngine *engine, int nameIndex)
+{
+    Scope scope(engine);
+    ScopedString name(scope, engine->currentStackFrame->v4Function->compilationUnit->runtimeStrings[nameIndex]);
+    engine->throwReferenceError(name);
+}
 
 void Runtime::method_declareVar(ExecutionEngine *engine, bool deletable, int nameIndex)
 {
diff --git a/src/qml/jsruntime/qv4runtimeapi_p.h b/src/qml/jsruntime/qv4runtimeapi_p.h
index 3f65e6c6d6..5dafeee6ce 100644
--- a/src/qml/jsruntime/qv4runtimeapi_p.h
+++ b/src/qml/jsruntime/qv4runtimeapi_p.h
@@ -115,6 +115,7 @@ struct ExceptionCheck<void (*)(QV4::NoThrowEngine *, A, B, C)> {
     F(ReturnedValue, loadElement, (ExecutionEngine *engine, const Value &object, const Value &index)) \
     F(ReturnedValue, loadSuperProperty, (ExecutionEngine *engine, const Value &property)) \
     F(void, storeSuperProperty, (ExecutionEngine *engine, const Value &property, const Value &value)) \
+    F(ReturnedValue, loadSuperConstructor, (ExecutionEngine *engine, const Value &t)) \
     \
     /* typeof */  \
     F(ReturnedValue, typeofValue, (ExecutionEngine *engine, const Value &val)) \
@@ -132,6 +133,7 @@ struct ExceptionCheck<void (*)(QV4::NoThrowEngine *, A, B, C)> {
     F(ReturnedValue, createScriptContext, (ExecutionEngine *engine, int index)) \
     F(ReturnedValue, cloneBlockContext, (ExecutionContext *previous)) \
     F(ReturnedValue, popScriptContext, (ExecutionEngine *engine)) \
+    F(void, throwReferenceError, (ExecutionEngine *engine, int nameIndex)) \
     \
     /* closures */ \
     F(ReturnedValue, closure, (ExecutionEngine *engine, int functionId)) \
diff --git a/src/qml/jsruntime/qv4setobject.cpp b/src/qml/jsruntime/qv4setobject.cpp
index 30e849bfed..65824926b9 100644
--- a/src/qml/jsruntime/qv4setobject.cpp
+++ b/src/qml/jsruntime/qv4setobject.cpp
@@ -46,17 +46,26 @@
 using namespace QV4;
 
 DEFINE_OBJECT_VTABLE(SetCtor);
+DEFINE_OBJECT_VTABLE(WeakSetCtor);
 DEFINE_OBJECT_VTABLE(SetObject);
 
+void Heap::WeakSetCtor::init(QV4::ExecutionContext *scope)
+{
+    Heap::FunctionObject::init(scope, QStringLiteral("WeakSet"));
+}
+
 void Heap::SetCtor::init(QV4::ExecutionContext *scope)
 {
     Heap::FunctionObject::init(scope, QStringLiteral("Set"));
 }
 
-ReturnedValue SetCtor::virtualCallAsConstructor(const FunctionObject *f, const Value *argv, int argc, const Value *)
+ReturnedValue WeakSetCtor::construct(const FunctionObject *f, const Value *argv, int argc, const Value *, bool isWeak)
 {
     Scope scope(f);
     Scoped<SetObject> a(scope, scope.engine->memoryManager->allocate<SetObject>());
+    if (isWeak)
+        a->setPrototypeOf(scope.engine->weakSetPrototype());
+    a->d()->isWeakSet = isWeak;
 
     if (argc > 0) {
         ScopedValue iterable(scope, argv[0]);
@@ -89,12 +98,74 @@ ReturnedValue SetCtor::virtualCallAsConstructor(const FunctionObject *f, const V
     return a.asReturnedValue();
 }
 
-ReturnedValue SetCtor::virtualCall(const FunctionObject *f, const Value *, const Value *, int)
+ReturnedValue WeakSetCtor::virtualCallAsConstructor(const FunctionObject *f, const Value *argv, int argc, const Value *newTarget)
+{
+    return construct(f, argv, argc, newTarget, true);
+}
+
+ReturnedValue WeakSetCtor::virtualCall(const FunctionObject *f, const Value *, const Value *, int)
 {
     Scope scope(f);
     return scope.engine->throwTypeError(QString::fromLatin1("Set requires new"));
 }
 
+ReturnedValue SetCtor::virtualCallAsConstructor(const FunctionObject *f, const Value *argv, int argc, const Value *newTarget)
+{
+    return construct(f, argv, argc, newTarget, false);
+}
+
+void WeakSetPrototype::init(ExecutionEngine *engine, Object *ctor)
+{
+    Scope scope(engine);
+    ScopedObject o(scope);
+    ctor->defineReadonlyConfigurableProperty(engine->id_length(), Primitive::fromInt32(0));
+    ctor->defineReadonlyProperty(engine->id_prototype(), (o = this));
+    defineDefaultProperty(engine->id_constructor(), (o = ctor));
+
+    defineDefaultProperty(QStringLiteral("add"), method_add, 1);
+    defineDefaultProperty(QStringLiteral("delete"), method_delete, 1);
+    defineDefaultProperty(QStringLiteral("has"), method_has, 1);
+
+    ScopedString val(scope, engine->newString(QLatin1String("WeakSet")));
+    defineReadonlyConfigurableProperty(engine->symbol_toStringTag(), val);
+}
+
+ReturnedValue WeakSetPrototype::method_add(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
+{
+    Scope scope(b);
+    Scoped<SetObject> that(scope, thisObject);
+    if ((!that || !that->d()->isWeakSet) ||
+        (!argc || !argv[0].isObject()))
+        return scope.engine->throwTypeError();
+
+    that->d()->esTable->set(argv[0], Primitive::undefinedValue());
+    return that.asReturnedValue();
+}
+
+ReturnedValue WeakSetPrototype::method_delete(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
+{
+    Scope scope(b);
+    Scoped<SetObject> that(scope, thisObject);
+    if (!that || !that->d()->isWeakSet)
+        return scope.engine->throwTypeError();
+    if (!argc || !argv[0].isObject())
+        return Encode(false);
+
+    return Encode(that->d()->esTable->remove(argv[0]));
+}
+
+ReturnedValue WeakSetPrototype::method_has(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
+{
+    Scope scope(b);
+    Scoped<SetObject> that(scope, thisObject);
+    if (!that || !that->d()->isWeakSet)
+        return scope.engine->throwTypeError();
+    if (!argc || !argv[0].isObject())
+        return Encode(false);
+
+    return Encode(that->d()->esTable->has(argv[0]));
+}
+
 void SetPrototype::init(ExecutionEngine *engine, Object *ctor)
 {
     Scope scope(engine);
@@ -136,10 +207,15 @@ void Heap::SetObject::destroy()
     esTable = 0;
 }
 
+void Heap::SetObject::removeUnmarkedKeys()
+{
+    esTable->removeUnmarkedKeys();
+}
+
 void Heap::SetObject::markObjects(Heap::Base *that, MarkStack *markStack)
 {
     SetObject *s = static_cast<SetObject *>(that);
-    s->esTable->markObjects(markStack);
+    s->esTable->markObjects(markStack, s->isWeakSet);
     Object::markObjects(that, markStack);
 }
 
@@ -147,7 +223,7 @@ ReturnedValue SetPrototype::method_add(const FunctionObject *b, const Value *thi
 {
     Scope scope(b);
     Scoped<SetObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakSet)
         return scope.engine->throwTypeError();
 
     that->d()->esTable->set(argv[0], Primitive::undefinedValue());
@@ -158,7 +234,7 @@ ReturnedValue SetPrototype::method_clear(const FunctionObject *b, const Value *t
 {
     Scope scope(b);
     Scoped<SetObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakSet)
         return scope.engine->throwTypeError();
 
     that->d()->esTable->clear();
@@ -169,7 +245,7 @@ ReturnedValue SetPrototype::method_delete(const FunctionObject *b, const Value *
 {
     Scope scope(b);
     Scoped<SetObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakSet)
         return scope.engine->throwTypeError();
 
     return Encode(that->d()->esTable->remove(argv[0]));
@@ -179,7 +255,7 @@ ReturnedValue SetPrototype::method_entries(const FunctionObject *b, const Value
 {
     Scope scope(b);
     Scoped<SetObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakSet)
         return scope.engine->throwTypeError();
 
     Scoped<SetIteratorObject> ao(scope, scope.engine->newSetIteratorObject(that));
@@ -191,7 +267,7 @@ ReturnedValue SetPrototype::method_forEach(const FunctionObject *b, const Value
 {
     Scope scope(b);
     Scoped<SetObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakSet)
         return scope.engine->throwTypeError();
 
     ScopedFunctionObject callbackfn(scope, argv[0]);
@@ -218,7 +294,7 @@ ReturnedValue SetPrototype::method_has(const FunctionObject *b, const Value *thi
 {
     Scope scope(b);
     Scoped<SetObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakSet)
         return scope.engine->throwTypeError();
 
     return Encode(that->d()->esTable->has(argv[0]));
@@ -228,7 +304,7 @@ ReturnedValue SetPrototype::method_get_size(const FunctionObject *b, const Value
 {
     Scope scope(b);
     Scoped<SetObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakSet)
         return scope.engine->throwTypeError();
 
     return Encode(that->d()->esTable->size());
@@ -238,11 +314,10 @@ ReturnedValue SetPrototype::method_values(const FunctionObject *b, const Value *
 {
     Scope scope(b);
     Scoped<SetObject> that(scope, thisObject);
-    if (!that)
+    if (!that || that->d()->isWeakSet)
         return scope.engine->throwTypeError();
 
     Scoped<SetIteratorObject> ao(scope, scope.engine->newSetIteratorObject(that));
     ao->d()->iterationKind = IteratorKind::ValueIteratorKind;
     return ao->asReturnedValue();
 }
-
diff --git a/src/qml/jsruntime/qv4setobject_p.h b/src/qml/jsruntime/qv4setobject_p.h
index 34649c3f01..21584e2132 100644
--- a/src/qml/jsruntime/qv4setobject_p.h
+++ b/src/qml/jsruntime/qv4setobject_p.h
@@ -64,7 +64,12 @@ class ESTable;
 
 namespace Heap {
 
-struct SetCtor : FunctionObject {
+struct WeakSetCtor : FunctionObject {
+    void init(QV4::ExecutionContext *scope);
+};
+
+
+struct SetCtor : WeakSetCtor {
     void init(QV4::ExecutionContext *scope);
 };
 
@@ -72,19 +77,33 @@ struct SetObject : Object {
     static void markObjects(Heap::Base *that, MarkStack *markStack);
     void init();
     void destroy();
+    void removeUnmarkedKeys();
+
     ESTable *esTable;
+    SetObject *nextWeakSet;
+    bool isWeakSet;
 };
 
 }
 
-struct SetCtor: FunctionObject
+
+struct WeakSetCtor: FunctionObject
 {
-    V4_OBJECT2(SetCtor, FunctionObject)
+    V4_OBJECT2(WeakSetCtor, FunctionObject)
+
+    static ReturnedValue construct(const FunctionObject *f, const Value *argv, int argc, const Value *, bool weakSet);
 
     static ReturnedValue virtualCallAsConstructor(const FunctionObject *f, const Value *argv, int argc, const Value *);
     static ReturnedValue virtualCall(const FunctionObject *f, const Value *thisObject, const Value *argv, int argc);
 };
 
+struct SetCtor : WeakSetCtor
+{
+    V4_OBJECT2(SetCtor, WeakSetCtor)
+
+    static ReturnedValue virtualCallAsConstructor(const FunctionObject *f, const Value *argv, int argc, const Value *);
+};
+
 struct SetObject : Object
 {
     V4_OBJECT2(SetObject, Object)
@@ -92,7 +111,17 @@ struct SetObject : Object
     V4_NEEDS_DESTROY
 };
 
-struct SetPrototype : Object
+struct WeakSetPrototype : Object
+{
+    void init(ExecutionEngine *engine, Object *ctor);
+
+    static ReturnedValue method_add(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
+    static ReturnedValue method_delete(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
+    static ReturnedValue method_has(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
+};
+
+
+struct SetPrototype : WeakSetPrototype
 {
     void init(ExecutionEngine *engine, Object *ctor);
 
diff --git a/src/qml/jsruntime/qv4stackframe_p.h b/src/qml/jsruntime/qv4stackframe_p.h
index 878f9283e7..ca39a8f7bb 100644
--- a/src/qml/jsruntime/qv4stackframe_p.h
+++ b/src/qml/jsruntime/qv4stackframe_p.h
@@ -181,6 +181,15 @@ struct Q_QML_EXPORT CppStackFrame {
         const Value *end = jsFrame->args + nRegisters;
         for (Value *v = jsFrame->args + argc; v < end; ++v)
             *v = Encode::undefined();
+
+        if (v4Function && v4Function->compiledFunction) {
+            const int firstDeadZoneRegister = v4Function->compiledFunction->firstTemporalDeadZoneRegister;
+            const int registerDeadZoneSize = v4Function->compiledFunction->sizeOfRegisterTemporalDeadZone;
+
+            const Value * tdzEnd = stackSpace + firstDeadZoneRegister + registerDeadZoneSize;
+            for (Value *v = stackSpace + firstDeadZoneRegister; v < tdzEnd; ++v)
+                *v = Primitive::emptyValue().asReturnedValue();
+        }
     }
 #endif
 
diff --git a/src/qml/jsruntime/qv4typedarray.cpp b/src/qml/jsruntime/qv4typedarray.cpp
index 7606af80cb..7492f8872d 100644
--- a/src/qml/jsruntime/qv4typedarray.cpp
+++ b/src/qml/jsruntime/qv4typedarray.cpp
@@ -467,6 +467,13 @@ ReturnedValue TypedArray::virtualGet(const Managed *m, PropertyKey id, const Val
     return a->d()->type->read(a->d()->buffer->data->data() + byteOffset);
 }
 
+bool TypedArray::virtualHasProperty(const Managed *m, PropertyKey id)
+{
+    bool hasProperty = false;
+    virtualGet(m, id, nullptr, &hasProperty);
+    return hasProperty;
+}
+
 bool TypedArray::virtualPut(Managed *m, PropertyKey id, const Value &value, Value *receiver)
 {
     if (!id.isArrayIndex())
diff --git a/src/qml/jsruntime/qv4typedarray_p.h b/src/qml/jsruntime/qv4typedarray_p.h
index d29599f31e..909334adb0 100644
--- a/src/qml/jsruntime/qv4typedarray_p.h
+++ b/src/qml/jsruntime/qv4typedarray_p.h
@@ -166,6 +166,7 @@ struct Q_QML_PRIVATE_EXPORT TypedArray : Object
     using Object::get;
 
     static ReturnedValue virtualGet(const Managed *m, PropertyKey id, const Value *receiver, bool *hasProperty);
+    static bool virtualHasProperty(const Managed *m, PropertyKey id);
     static bool virtualPut(Managed *m, PropertyKey id, const Value &value, Value *receiver);
 };
 
diff --git a/src/qml/jsruntime/qv4vme_moth.cpp b/src/qml/jsruntime/qv4vme_moth.cpp
index aed3fce6b1..fd2328beaa 100644
--- a/src/qml/jsruntime/qv4vme_moth.cpp
+++ b/src/qml/jsruntime/qv4vme_moth.cpp
@@ -784,6 +784,15 @@ QV4::ReturnedValue VME::interpret(CppStackFrame *frame, ExecutionEngine *engine,
         goto handleUnwind;
     MOTH_END_INSTR(UnwindToLabel)
 
+    MOTH_BEGIN_INSTR(DeadTemporalZoneCheck)
+        if (ACC.isEmpty()) {
+            STORE_IP();
+            STORE_ACC();
+            Runtime::method_throwReferenceError(engine, name);
+            goto handleUnwind;
+        }
+    MOTH_END_INSTR(DeadTemporalZoneCheck)
+
     MOTH_BEGIN_INSTR(ThrowException)
         STORE_IP();
         STORE_ACC();
@@ -949,12 +958,7 @@ QV4::ReturnedValue VME::interpret(CppStackFrame *frame, ExecutionEngine *engine,
     MOTH_END_INSTR(ConvertThisToObject)
 
     MOTH_BEGIN_INSTR(LoadSuperConstructor)
-        const FunctionObject *f = stack[CallData::Function].as<FunctionObject>();
-        if (!f || !f->isConstructor()) {
-            engine->throwTypeError();
-        } else {
-            acc = static_cast<const Object *>(f)->getPrototypeOf()->asReturnedValue();
-        }
+        acc = Runtime::method_loadSuperConstructor(engine, stack[CallData::Function]);
         CHECK_EXCEPTION;
     MOTH_END_INSTR(LoadSuperConstructor)
 
@@ -1322,6 +1326,12 @@ QV4::ReturnedValue VME::interpret(CppStackFrame *frame, ExecutionEngine *engine,
         return acc;
     MOTH_END_INSTR(Ret)
 
+    MOTH_BEGIN_INSTR(InitializeBlockDeadTemporalZone)
+        acc = Encode(Primitive::emptyValue());
+        for (int i = firstReg, end = firstReg + count; i < end; ++i)
+            STACK_VALUE(i) = acc;
+    MOTH_END_INSTR(InitializeBlockDeadTemporalZone)
+
     MOTH_BEGIN_INSTR(Debug)
 #if QT_CONFIG(qml_debug)
         STORE_IP();
diff --git a/src/qml/memory/qv4mm.cpp b/src/qml/memory/qv4mm.cpp
index 258fac57af..b9e6327ea2 100644
--- a/src/qml/memory/qv4mm.cpp
+++ b/src/qml/memory/qv4mm.cpp
@@ -61,6 +61,8 @@
 #include <algorithm>
 #include "qv4alloca_p.h"
 #include "qv4profiling_p.h"
+#include "qv4mapobject_p.h"
+#include "qv4setobject_p.h"
 
 //#define MM_STATS
 
@@ -976,6 +978,29 @@ void MemoryManager::sweep(bool lastSweep, ClassDestroyStatsCallback classCountPt
         (*it) = Primitive::undefinedValue();
     }
 
+    // remove objects from weak maps and sets
+    Heap::MapObject *map = weakMaps;
+    Heap::MapObject **lastMap = &weakMaps;
+    while (map) {
+        if (map->isMarked()) {
+            map->removeUnmarkedKeys();
+            *lastMap = map;
+            lastMap = &map->nextWeakMap;
+        }
+        map = map->nextWeakMap;
+    }
+
+    Heap::SetObject *set = weakSets;
+    Heap::SetObject **lastSet = &weakSets;
+    while (set) {
+        if (set->isMarked()) {
+            set->removeUnmarkedKeys();
+            *lastSet = set;
+            lastSet = &set->nextWeakSet;
+        }
+        set = set->nextWeakSet;
+    }
+
     // onDestruction handlers may have accessed other QObject wrappers and reset their value, so ensure
     // that they are all set to undefined.
     for (PersistentValueStorage::Iterator it = m_weakValues->begin(); it != m_weakValues->end(); ++it) {
@@ -1179,6 +1204,18 @@ size_t MemoryManager::getLargeItemsMem() const
     return hugeItemAllocator.usedMem();
 }
 
+void MemoryManager::registerWeakMap(Heap::MapObject *map)
+{
+    map->nextWeakMap = weakMaps;
+    weakMaps = map;
+}
+
+void MemoryManager::registerWeakSet(Heap::SetObject *set)
+{
+    set->nextWeakSet = weakSets;
+    weakSets = set;
+}
+
 MemoryManager::~MemoryManager()
 {
     delete m_persistentValues;
diff --git a/src/qml/memory/qv4mm_p.h b/src/qml/memory/qv4mm_p.h
index e3a011caf9..bbbbb1aef6 100644
--- a/src/qml/memory/qv4mm_p.h
+++ b/src/qml/memory/qv4mm_p.h
@@ -274,6 +274,9 @@ public:
         return static_cast<typename ManagedType::Data *>(b);
     }
 
+    void registerWeakMap(Heap::MapObject *map);
+    void registerWeakSet(Heap::SetObject *set);
+
 protected:
     /// expects size to be aligned
     Heap::Base *allocString(std::size_t unmanagedSize);
@@ -296,6 +299,8 @@ public:
     PersistentValueStorage *m_persistentValues;
     PersistentValueStorage *m_weakValues;
     QVector<Value *> m_pendingFreedObjectWrapperValue;
+    Heap::MapObject *weakMaps = nullptr;
+    Heap::SetObject *weakSets = nullptr;
 
     std::size_t unmanagedHeapSize = 0; // the amount of bytes of heap that is not managed by the memory manager, but which is held onto by managed items.
     std::size_t unmanagedHeapSizeGCLimit;
diff --git a/tests/auto/qml/ecmascripttests/TestExpectations b/tests/auto/qml/ecmascripttests/TestExpectations
index b303592e23..f9a405db6d 100644
--- a/tests/auto/qml/ecmascripttests/TestExpectations
+++ b/tests/auto/qml/ecmascripttests/TestExpectations
@@ -27,8 +27,6 @@ language/module-code/namespace/internals/set.js strictFails
 
 # ----- test failures that should be fixed
 built-ins/Array/from/proto-from-ctor-realm.js fails
-built-ins/Array/isArray/proxy-revoked.js fails
-built-ins/Array/isArray/proxy.js fails
 built-ins/Array/length/define-own-prop-length-overflow-realm.js fails
 built-ins/Array/of/proto-from-ctor-realm.js fails
 built-ins/Array/proto-from-ctor-realm.js fails
@@ -205,36 +203,8 @@ built-ins/JSON/parse/revived-proxy.js fails
 built-ins/JSON/stringify/replacer-proxy-revoked.js fails
 built-ins/JSON/stringify/replacer-proxy.js fails
 built-ins/JSON/stringify/value-proxy.js fails
-built-ins/Map/iterable-calls-set.js fails
-built-ins/Map/iterator-close-after-set-failure.js fails
-built-ins/Map/iterator-is-undefined-throws.js fails
-built-ins/Map/iterator-item-first-entry-returns-abrupt.js fails
-built-ins/Map/iterator-item-second-entry-returns-abrupt.js fails
-built-ins/Map/iterator-items-are-not-object-close-iterator.js fails
-built-ins/Map/iterator-items-are-not-object.js fails
-built-ins/Map/map-iterable-throws-when-set-is-not-callable.js fails
-built-ins/Map/map-iterable.js fails
 built-ins/Map/proto-from-ctor-realm.js fails
-built-ins/Map/prototype/clear/context-is-weakmap-object-throws.js fails
-built-ins/Map/prototype/delete/context-is-weakmap-object-throws.js fails
-built-ins/Map/prototype/delete/does-not-break-iterators.js fails
-built-ins/Map/prototype/delete/returns-true-for-deleted-entry.js fails
-built-ins/Map/prototype/entries/does-not-have-mapdata-internal-slot-weakmap.js fails
-built-ins/Map/prototype/forEach/callback-parameters.js fails
-built-ins/Map/prototype/forEach/deleted-values-during-foreach.js fails
-built-ins/Map/prototype/forEach/does-not-have-mapdata-internal-slot-weakmap.js fails
-built-ins/Map/prototype/forEach/iterates-in-key-insertion-order.js fails
-built-ins/Map/prototype/forEach/iterates-values-added-after-foreach-begins.js fails
 built-ins/Map/prototype/forEach/iterates-values-deleted-then-readded.js fails
-built-ins/Map/prototype/get/does-not-have-mapdata-internal-slot-weakmap.js fails
-built-ins/Map/prototype/has/does-not-have-mapdata-internal-slot-weakmap.js fails
-built-ins/Map/prototype/keys/does-not-have-mapdata-internal-slot-weakmap.js fails
-built-ins/Map/prototype/set/append-new-values.js fails
-built-ins/Map/prototype/set/does-not-have-mapdata-internal-slot-weakmap.js fails
-built-ins/Map/prototype/set/length.js fails
-built-ins/Map/prototype/size/does-not-have-mapdata-internal-slot-weakmap.js fails
-built-ins/Map/prototype/size/returns-count-of-present-values-by-iterable.js fails
-built-ins/Map/prototype/values/does-not-have-mapdata-internal-slot-weakmap.js fails
 built-ins/Math/max/zeros.js fails
 built-ins/Math/round/S15.8.2.15_A7.js fails
 built-ins/Number/isFinite/arg-is-not-number.js fails
@@ -489,15 +459,8 @@ built-ins/RegExp/unicode_restricted_octal_escape.js fails
 built-ins/RegExp/unicode_restricted_quantifiable_assertion.js fails
 built-ins/RegExp/u180e.js fails
 built-ins/Set/proto-from-ctor-realm.js fails
-built-ins/Set/prototype/add/does-not-have-setdata-internal-slot-weakset.js fails
-built-ins/Set/prototype/clear/does-not-have-setdata-internal-slot-weakset.js fails
-built-ins/Set/prototype/delete/does-not-have-setdata-internal-slot-weakset.js fails
-built-ins/Set/prototype/entries/does-not-have-setdata-internal-slot-weakset.js fails
-built-ins/Set/prototype/forEach/does-not-have-setdata-internal-slot-weakset.js fails
 built-ins/Set/prototype/forEach/iterates-values-revisits-after-delete-re-add.js fails
 built-ins/Set/prototype/forEach/this-arg-explicit-cannot-override-lexical-this-arrow.js fails
-built-ins/Set/prototype/has/does-not-have-setdata-internal-slot-weakset.js fails
-built-ins/Set/prototype/values/does-not-have-setdata-internal-slot-weakset.js fails
 built-ins/SharedArrayBuffer/data-allocation-after-object-creation.js fails
 built-ins/SharedArrayBuffer/proto-from-ctor-realm.js fails
 built-ins/SharedArrayBuffer/prototype-from-newtarget.js fails
@@ -657,169 +620,8 @@ built-ins/TypedArrays/internals/Set/key-is-minus-zero.js fails
 built-ins/TypedArrays/internals/Set/key-is-not-integer.js fails
 built-ins/TypedArrays/internals/Set/key-is-out-of-bounds.js fails
 built-ins/TypedArrays/internals/Set/tonumber-value-throws.js strictFails
-built-ins/WeakMap/constructor.js fails
-built-ins/WeakMap/empty-iterable.js fails
-built-ins/WeakMap/get-set-method-failure.js fails
-built-ins/WeakMap/iterable-failure.js fails
-built-ins/WeakMap/iterable.js fails
-built-ins/WeakMap/iterator-close-after-set-failure.js fails
-built-ins/WeakMap/iterator-item-first-entry-returns-abrupt.js fails
-built-ins/WeakMap/iterator-item-second-entry-returns-abrupt.js fails
-built-ins/WeakMap/iterator-items-are-not-object-close-iterator.js fails
-built-ins/WeakMap/iterator-items-are-not-object.js fails
-built-ins/WeakMap/iterator-next-failure.js fails
-built-ins/WeakMap/iterator-value-failure.js fails
-built-ins/WeakMap/length.js fails
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-built-ins/WeakMap/no-iterable.js fails
-built-ins/WeakMap/properties-of-map-instances.js fails
-built-ins/WeakMap/properties-of-the-weakmap-prototype-object.js fails
 built-ins/WeakMap/proto-from-ctor-realm.js fails
-built-ins/WeakMap/prototype-of-weakmap.js fails
-built-ins/WeakMap/prototype/Symbol.toStringTag.js fails
-built-ins/WeakMap/prototype/constructor.js fails
-built-ins/WeakMap/prototype/delete/delete-entry-initial-iterable.js fails
-built-ins/WeakMap/prototype/delete/delete-entry.js fails
-built-ins/WeakMap/prototype/delete/delete.js fails
-built-ins/WeakMap/prototype/delete/does-not-have-weakmapdata-internal-slot-array.js fails
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-built-ins/WeakMap/prototype/delete/does-not-have-weakmapdata-internal-slot-object.js fails
-built-ins/WeakMap/prototype/delete/does-not-have-weakmapdata-internal-slot-set.js fails
-built-ins/WeakMap/prototype/delete/does-not-have-weakmapdata-internal-slot-weakmap-prototype.js fails
-built-ins/WeakMap/prototype/delete/length.js fails
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-built-ins/WeakMap/prototype/delete/returns-false-when-delete-is-noop.js fails
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-built-ins/WeakMap/set-not-callable-throws.js fails
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-built-ins/WeakMap/weakmap.js fails
-built-ins/WeakSet/add-not-callable-throws.js fails
-built-ins/WeakSet/constructor.js fails
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-built-ins/WeakSet/name.js fails
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-built-ins/WeakSet/properties-of-the-weakset-prototype-object.js fails
 built-ins/WeakSet/proto-from-ctor-realm.js fails
-built-ins/WeakSet/prototype-of-weakset.js fails
-built-ins/WeakSet/prototype/Symbol.toStringTag.js fails
-built-ins/WeakSet/prototype/add/add.js fails
-built-ins/WeakSet/prototype/add/adds-element.js fails
-built-ins/WeakSet/prototype/add/does-not-have-weaksetdata-internal-slot-array.js fails
-built-ins/WeakSet/prototype/add/does-not-have-weaksetdata-internal-slot-map.js fails
-built-ins/WeakSet/prototype/add/does-not-have-weaksetdata-internal-slot-object.js fails
-built-ins/WeakSet/prototype/add/does-not-have-weaksetdata-internal-slot-set.js fails
-built-ins/WeakSet/prototype/add/does-not-have-weaksetdata-internal-slot-weakset-prototype.js fails
-built-ins/WeakSet/prototype/add/length.js fails
-built-ins/WeakSet/prototype/add/name.js fails
-built-ins/WeakSet/prototype/add/returns-this-when-ignoring-duplicate.js fails
-built-ins/WeakSet/prototype/add/returns-this.js fails
-built-ins/WeakSet/prototype/add/this-not-object-throw-boolean.js fails
-built-ins/WeakSet/prototype/add/this-not-object-throw-null.js fails
-built-ins/WeakSet/prototype/add/this-not-object-throw-number.js fails
-built-ins/WeakSet/prototype/add/this-not-object-throw-string.js fails
-built-ins/WeakSet/prototype/add/this-not-object-throw-symbol.js fails
-built-ins/WeakSet/prototype/add/this-not-object-throw-undefined.js fails
-built-ins/WeakSet/prototype/add/value-not-object-throw.js fails
-built-ins/WeakSet/prototype/constructor/weakset-prototype-constructor-intrinsic.js fails
-built-ins/WeakSet/prototype/constructor/weakset-prototype-constructor.js fails
-built-ins/WeakSet/prototype/delete/delete-entry-initial-iterable.js fails
-built-ins/WeakSet/prototype/delete/delete-entry.js fails
-built-ins/WeakSet/prototype/delete/delete.js fails
-built-ins/WeakSet/prototype/delete/does-not-have-weaksetdata-internal-slot-array.js fails
-built-ins/WeakSet/prototype/delete/does-not-have-weaksetdata-internal-slot-map.js fails
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-built-ins/WeakSet/prototype/delete/does-not-have-weaksetdata-internal-slot-set.js fails
-built-ins/WeakSet/prototype/delete/does-not-have-weaksetdata-internal-slot-weakset-prototype.js fails
-built-ins/WeakSet/prototype/delete/length.js fails
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-built-ins/WeakSet/prototype/delete/returns-false-value-is-not-object.js fails
-built-ins/WeakSet/prototype/delete/returns-false-when-delete-is-noop.js fails
-built-ins/WeakSet/prototype/delete/this-not-object-throw-boolean.js fails
-built-ins/WeakSet/prototype/delete/this-not-object-throw-null.js fails
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-built-ins/WeakSet/prototype/delete/this-not-object-throw-string.js fails
-built-ins/WeakSet/prototype/delete/this-not-object-throw-symbol.js fails
-built-ins/WeakSet/prototype/delete/this-not-object-throw-undefined.js fails
-built-ins/WeakSet/prototype/has/does-not-have-weaksetdata-internal-slot-array.js fails
-built-ins/WeakSet/prototype/has/does-not-have-weaksetdata-internal-slot-map.js fails
-built-ins/WeakSet/prototype/has/does-not-have-weaksetdata-internal-slot-object.js fails
-built-ins/WeakSet/prototype/has/does-not-have-weaksetdata-internal-slot-set.js fails
-built-ins/WeakSet/prototype/has/does-not-have-weaksetdata-internal-slot-weakset-prototype.js fails
-built-ins/WeakSet/prototype/has/has.js fails
-built-ins/WeakSet/prototype/has/length.js fails
-built-ins/WeakSet/prototype/has/name.js fails
-built-ins/WeakSet/prototype/has/returns-false-when-value-is-not-object.js fails
-built-ins/WeakSet/prototype/has/returns-false-when-value-not-present.js fails
-built-ins/WeakSet/prototype/has/returns-true-when-value-present.js fails
-built-ins/WeakSet/prototype/has/this-not-object-throw-boolean.js fails
-built-ins/WeakSet/prototype/has/this-not-object-throw-null.js fails
-built-ins/WeakSet/prototype/has/this-not-object-throw-number.js fails
-built-ins/WeakSet/prototype/has/this-not-object-throw-string.js fails
-built-ins/WeakSet/prototype/has/this-not-object-throw-symbol.js fails
-built-ins/WeakSet/prototype/has/this-not-object-throw-undefined.js fails
-built-ins/WeakSet/prototype/prototype-attributes.js fails
-built-ins/WeakSet/symbol-disallowed-as-weakset-key.js fails
-built-ins/WeakSet/undefined-newtarget.js fails
-built-ins/WeakSet/weakset.js fails
 built-ins/global/global-object.js fails
 built-ins/global/property-descriptor.js fails
 built-ins/isFinite/toprimitive-not-callable-throws.js fails
@@ -827,9 +629,6 @@ built-ins/isNaN/toprimitive-not-callable-throws.js fails
 language/computed-property-names/class/static/method-number.js fails
 language/computed-property-names/class/static/method-string.js fails
 language/computed-property-names/class/static/method-symbol.js fails
-language/eval-code/direct/lex-env-no-init-cls.js fails
-language/eval-code/direct/lex-env-no-init-const.js fails
-language/eval-code/direct/lex-env-no-init-let.js fails
 language/eval-code/direct/new.target.js fails
 language/eval-code/direct/new.target-arrow.js fails
 language/eval-code/direct/new.target-fn.js fails
@@ -852,9 +651,6 @@ language/eval-code/direct/var-env-global-lex-non-strict.js sloppyFails
 language/eval-code/direct/var-env-lower-lex-catch-non-strict.js sloppyFails
 language/eval-code/direct/var-env-lower-lex-non-strict.js sloppyFails
 language/eval-code/indirect/always-non-strict.js strictFails
-language/eval-code/indirect/lex-env-no-init-cls.js fails
-language/eval-code/indirect/lex-env-no-init-const.js fails
-language/eval-code/indirect/lex-env-no-init-let.js fails
 language/eval-code/indirect/new.target.js fails
 language/eval-code/indirect/non-definable-function-with-function.js sloppyFails
 language/eval-code/indirect/non-definable-function-with-variable.js sloppyFails
@@ -904,7 +700,6 @@ language/expressions/assignment/S11.13.1_A7_T2.js fails
 language/expressions/assignment/S11.13.1_A7_T3.js fails
 language/expressions/assignment/destructuring/iterator-destructuring-property-reference-target-evaluation-order.js fails
 language/expressions/assignment/destructuring/keyed-destructuring-property-reference-target-evaluation-order.js fails
-language/expressions/assignment/dstr-array-elem-init-let.js fails
 language/expressions/assignment/dstr-array-elem-iter-rtrn-close-err.js fails
 language/expressions/assignment/dstr-array-elem-iter-rtrn-close-null.js fails
 language/expressions/assignment/dstr-array-elem-iter-rtrn-close.js fails
@@ -930,9 +725,7 @@ language/expressions/assignment/dstr-array-rest-lref-err.js fails
 language/expressions/assignment/dstr-array-rest-put-let.js fails
 language/expressions/assignment/dstr-obj-empty-null.js fails
 language/expressions/assignment/dstr-obj-empty-undef.js fails
-language/expressions/assignment/dstr-obj-id-init-let.js fails
 language/expressions/assignment/dstr-obj-id-put-let.js fails
-language/expressions/assignment/dstr-obj-prop-elem-init-let.js fails
 language/expressions/assignment/dstr-obj-prop-put-let.js fails
 language/expressions/assignment/fn-name-lhs-cover.js fails
 language/expressions/assignment/fn-name-lhs-member.js fails
@@ -1092,8 +885,6 @@ language/expressions/generators/yield-identifier-non-strict.js sloppyFails
 language/expressions/generators/yield-star-before-newline.js fails
 language/expressions/logical-and/tco-right.js strictFails
 language/expressions/logical-or/tco-right.js strictFails
-language/expressions/new.target/value-via-super-call.js fails
-language/expressions/new.target/value-via-super-property.js fails
 language/expressions/new/non-ctor-err-realm.js fails
 language/expressions/object/let-non-strict-access.js sloppyFails
 language/expressions/object/let-non-strict-syntax.js sloppyFails
@@ -1150,27 +941,18 @@ language/expressions/prefix-increment/S11.4.4_A5_T3.js sloppyFails
 language/expressions/prefix-increment/S11.4.4_A5_T4.js sloppyFails
 language/expressions/prefix-increment/S11.4.4_A5_T5.js fails
 language/expressions/prefix-increment/S11.4.4_A6_T3.js fails
-language/expressions/super/call-bind-this-value-twice.js fails
-language/expressions/super/call-construct-invocation.js fails
-language/expressions/super/call-proto-not-ctor.js fails
-language/expressions/super/prop-dot-cls-null-proto.js fails
 language/expressions/super/prop-dot-cls-ref-strict.js fails
 language/expressions/super/prop-dot-cls-ref-this.js fails
 language/expressions/super/prop-dot-cls-this-uninit.js fails
 language/expressions/super/prop-dot-cls-val-from-arrow.js fails
-language/expressions/super/prop-dot-obj-null-proto.js fails
 language/expressions/super/prop-dot-obj-ref-non-strict.js sloppyFails
 language/expressions/super/prop-dot-obj-ref-strict.js strictFails
 language/expressions/super/prop-dot-obj-ref-this.js fails
 language/expressions/super/prop-dot-obj-val-from-arrow.js fails
-language/expressions/super/prop-expr-cls-key-err.js fails
-language/expressions/super/prop-expr-cls-null-proto.js fails
 language/expressions/super/prop-expr-cls-ref-strict.js fails
 language/expressions/super/prop-expr-cls-ref-this.js fails
 language/expressions/super/prop-expr-cls-this-uninit.js fails
 language/expressions/super/prop-expr-cls-val-from-arrow.js fails
-language/expressions/super/prop-expr-obj-key-err.js fails
-language/expressions/super/prop-expr-obj-null-proto.js fails
 language/expressions/super/prop-expr-obj-ref-non-strict.js sloppyFails
 language/expressions/super/prop-expr-obj-ref-strict.js strictFails
 language/expressions/super/prop-expr-obj-ref-this.js fails
@@ -1256,29 +1038,6 @@ language/global-code/script-decl-var.js fails
 language/identifiers/other_id_continue.js fails
 language/identifiers/other_id_start-escaped.js fails
 language/identifiers/other_id_start.js fails
-language/module-code/instn-iee-bndng-cls.js strictFails
-language/module-code/instn-iee-bndng-const.js strictFails
-language/module-code/instn-iee-bndng-let.js strictFails
-language/module-code/instn-local-bndng-cls.js strictFails
-language/module-code/instn-local-bndng-const.js strictFails
-language/module-code/instn-local-bndng-export-cls.js strictFails
-language/module-code/instn-local-bndng-export-const.js strictFails
-language/module-code/instn-local-bndng-export-let.js strictFails
-language/module-code/instn-local-bndng-let.js strictFails
-language/module-code/instn-named-bndng-cls.js strictFails
-language/module-code/instn-named-bndng-const.js strictFails
-language/module-code/instn-named-bndng-dflt-cls.js strictFails
-language/module-code/instn-named-bndng-dflt-expr.js strictFails
-language/module-code/instn-named-bndng-dflt-named.js strictFails
-language/module-code/instn-named-bndng-dflt-star.js strictFails
-language/module-code/instn-named-bndng-let.js strictFails
-language/module-code/namespace/internals/delete-exported-uninit.js strictFails
-language/module-code/namespace/internals/enumerate-binding-uninit.js strictFails
-language/module-code/namespace/internals/get-own-property-str-found-uninit.js strictFails
-language/module-code/namespace/internals/get-str-found-uninit.js strictFails
-language/module-code/namespace/internals/object-hasOwnProperty-binding-uninit.js strictFails
-language/module-code/namespace/internals/object-keys-binding-uninit.js strictFails
-language/module-code/namespace/internals/object-propertyIsEnumerable-binding-uninit.js strictFails
 language/statements/async-function/cptn-decl.js fails
 language/statements/async-function/declaration-returns-promise.js fails
 language/statements/async-function/evaluation-body.js fails
@@ -1301,7 +1060,6 @@ language/statements/class/definition/numeric-property-names.js fails
 language/statements/class/definition/prototype-getter.js fails
 language/statements/class/definition/prototype-property.js fails
 language/statements/class/definition/prototype-setter.js fails
-language/statements/class/definition/prototype-wiring.js fails
 language/statements/class/definition/setters-prop-desc.js fails
 language/statements/class/definition/setters-restricted-ids.js fails
 language/statements/class/definition/this-access-restriction-2.js fails
@@ -1315,9 +1073,6 @@ language/statements/class/meth-dflt-params-ref-later.js fails
 language/statements/class/meth-dflt-params-ref-self.js fails
 language/statements/class/meth-static-dflt-params-ref-later.js fails
 language/statements/class/meth-static-dflt-params-ref-self.js fails
-language/statements/class/name-binding/in-extends-expression-assigned.js fails
-language/statements/class/name-binding/in-extends-expression-grouped.js fails
-language/statements/class/name-binding/in-extends-expression.js fails
 language/statements/class/scope-gen-meth-paramsbody-var-open.js fails
 language/statements/class/scope-meth-paramsbody-var-open.js fails
 language/statements/class/scope-setter-paramsbody-var-open.js fails
@@ -1334,7 +1089,6 @@ language/statements/class/subclass/builtin-objects/Date/super-must-be-called.js
 language/statements/class/subclass/builtin-objects/Error/super-must-be-called.js fails
 language/statements/class/subclass/builtin-objects/Function/super-must-be-called.js fails
 language/statements/class/subclass/builtin-objects/GeneratorFunction/super-must-be-called.js fails
-language/statements/class/subclass/builtin-objects/Map/regular-subclassing.js fails
 language/statements/class/subclass/builtin-objects/Map/super-must-be-called.js fails
 language/statements/class/subclass/builtin-objects/NativeError/EvalError-super.js fails
 language/statements/class/subclass/builtin-objects/NativeError/RangeError-super.js fails
@@ -1350,36 +1104,18 @@ language/statements/class/subclass/builtin-objects/RegExp/super-must-be-called.j
 language/statements/class/subclass/builtin-objects/Set/super-must-be-called.js fails
 language/statements/class/subclass/builtin-objects/String/super-must-be-called.js fails
 language/statements/class/subclass/builtin-objects/TypedArray/super-must-be-called.js fails
-language/statements/class/subclass/builtin-objects/WeakMap/regular-subclassing.js fails
 language/statements/class/subclass/builtin-objects/WeakMap/super-must-be-called.js fails
-language/statements/class/subclass/builtin-objects/WeakSet/regular-subclassing.js fails
 language/statements/class/subclass/builtin-objects/WeakSet/super-must-be-called.js fails
 language/statements/class/subclass/builtins.js fails
-language/statements/class/subclass/class-definition-null-proto-super.js fails
 language/statements/class/subclass/class-definition-null-proto-this.js fails
 language/statements/class/subclass/default-constructor-spread-override.js fails
 language/statements/class/super/in-methods.js fails
-language/statements/const/block-local-closure-get-before-initialization.js fails
-language/statements/const/block-local-use-before-initialization-in-declaration-statement.js fails
-language/statements/const/block-local-use-before-initialization-in-prior-statement.js fails
-language/statements/const/function-local-closure-get-before-initialization.js fails
-language/statements/const/function-local-use-before-initialization-in-declaration-statement.js fails
-language/statements/const/function-local-use-before-initialization-in-prior-statement.js fails
-language/statements/const/global-closure-get-before-initialization.js fails
-language/statements/const/global-use-before-initialization-in-declaration-statement.js fails
-language/statements/const/global-use-before-initialization-in-prior-statement.js fails
 language/statements/do-while/tco-body.js strictFails
-language/statements/for-in/head-const-bound-names-fordecl-tdz.js fails
-language/statements/for-in/head-let-bound-names-fordecl-tdz.js fails
 language/statements/for-in/head-lhs-let.js sloppyFails
 language/statements/for-in/head-var-bound-names-let.js sloppyFails
 language/statements/for-in/identifier-let-allowed-as-lefthandside-expression-not-strict.js sloppyFails
-language/statements/for-in/scope-body-lex-open.js fails
-language/statements/for-in/scope-head-lex-close.js fails
-language/statements/for-in/scope-head-lex-open.js fails
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 language/statements/for-of/body-put-error.js fails
-language/statements/for-of/dstr-array-elem-init-let.js fails
 language/statements/for-of/dstr-array-elem-iter-rtrn-close-err.js fails
 language/statements/for-of/dstr-array-elem-iter-rtrn-close-null.js fails
 language/statements/for-of/dstr-array-elem-iter-rtrn-close.js fails
@@ -1405,23 +1141,16 @@ language/statements/for-of/dstr-array-rest-lref-err.js fails
 language/statements/for-of/dstr-array-rest-put-let.js fails
 language/statements/for-of/dstr-obj-empty-null.js fails
 language/statements/for-of/dstr-obj-empty-undef.js fails
-language/statements/for-of/dstr-obj-id-init-let.js fails
 language/statements/for-of/dstr-obj-id-put-let.js fails
-language/statements/for-of/dstr-obj-prop-elem-init-let.js fails
 language/statements/for-of/dstr-obj-prop-put-let.js fails
 language/statements/for-of/generator-close-via-continue.js fails
 language/statements/for-of/generator-close-via-return.js fails
 language/statements/for-of/generator-close-via-throw.js fails
-language/statements/for-of/head-const-bound-names-fordecl-tdz.js fails
-language/statements/for-of/head-let-bound-names-fordecl-tdz.js fails
 language/statements/for-of/head-var-bound-names-let.js sloppyFails
 language/statements/for-of/iterator-close-via-continue.js fails
 language/statements/for-of/iterator-close-via-return.js fails
 language/statements/for-of/iterator-close-via-throw.js fails
 language/statements/for-of/iterator-next-reference.js fails
-language/statements/for-of/scope-body-lex-open.js fails
-language/statements/for-of/scope-head-lex-close.js fails
-language/statements/for-of/scope-head-lex-open.js fails
 language/statements/for-of/yield-star-from-catch.js fails
 language/statements/for-of/yield-star-from-finally.js fails
 language/statements/for-of/yield-star-from-try.js fails
@@ -1465,19 +1194,9 @@ language/statements/generators/yield-star-before-newline.js fails
 language/statements/if/tco-else-body.js strictFails
 language/statements/if/tco-if-body.js strictFails
 language/statements/labeled/tco.js strictFails
-language/statements/let/block-local-closure-get-before-initialization.js fails
 language/statements/let/block-local-closure-set-before-initialization.js fails
-language/statements/let/block-local-use-before-initialization-in-declaration-statement.js fails
-language/statements/let/block-local-use-before-initialization-in-prior-statement.js fails
-language/statements/let/function-local-closure-get-before-initialization.js fails
 language/statements/let/function-local-closure-set-before-initialization.js fails
-language/statements/let/function-local-use-before-initialization-in-declaration-statement.js fails
-language/statements/let/function-local-use-before-initialization-in-prior-statement.js fails
-language/statements/let/global-closure-get-before-initialization.js fails
 language/statements/let/global-closure-set-before-initialization.js fails
-language/statements/let/global-use-before-initialization-in-declaration-statement.js fails
-language/statements/let/global-use-before-initialization-in-prior-statement.js fails
-language/statements/let/syntax/let.js fails
 language/statements/return/tco.js strictFails
 language/statements/switch/scope-lex-open-case.js fails
 language/statements/switch/scope-lex-open-dflt.js fails
diff --git a/tests/auto/qml/qjsengine/tst_qjsengine.cpp b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
index 7ea652e070..f08d9a4798 100644
--- a/tests/auto/qml/qjsengine/tst_qjsengine.cpp
+++ b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
@@ -978,7 +978,9 @@ void tst_QJSEngine::globalObjectProperties_enumerate()
         << "Uint32Array"
         << "Float32Array"
         << "Float64Array"
+        << "WeakSet"
         << "Set"
+        << "WeakMap"
         << "Map"
         << "Reflect"
         << "Proxy"
diff --git a/tests/auto/qml/qml.pro b/tests/auto/qml/qml.pro
index 1bd23573b0..4d9e5c23c5 100644
--- a/tests/auto/qml/qml.pro
+++ b/tests/auto/qml/qml.pro
@@ -73,7 +73,8 @@ PRIVATETESTS += \
     qv4mm \
     qv4identifiertable \
     ecmascripttests \
-    bindingdependencyapi
+    bindingdependencyapi \
+    v4misc
 
 qtHaveModule(widgets) {
     PUBLICTESTS += \
diff --git a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
index 69b62c733c..99306d8d15 100644
--- a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
+++ b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
@@ -356,6 +356,7 @@ private slots:
     void callPropertyOnUndefined();
     void jumpStrictNotEqualUndefined();
     void removeBindingsWithNoDependencies();
+    void temporaryDeadZone();
 
 private:
 //    static void propertyVarWeakRefCallback(v8::Persistent<v8::Value> object, void* parameter);
@@ -8798,6 +8799,19 @@ void tst_qqmlecmascript::removeBindingsWithNoDependencies()
 
 }
 
+void tst_qqmlecmascript::temporaryDeadZone()
+{
+    QJSEngine engine;
+    QJSValue v = engine.evaluate(QString::fromLatin1("a; let a;"));
+    QVERIFY(v.isError());
+    v = engine.evaluate(QString::fromLatin1("a.name; let a;"));
+    QVERIFY(v.isError());
+    v = engine.evaluate(QString::fromLatin1("var a = {}; a[b]; let b;"));
+    QVERIFY(v.isError());
+    v = engine.evaluate(QString::fromLatin1("class C { constructor() { super[x]; let x; } }; new C()"));
+    QVERIFY(v.isError());
+}
+
 QTEST_MAIN(tst_qqmlecmascript)
 
 #include "tst_qqmlecmascript.moc"
diff --git a/tests/auto/qml/v4misc/tst_v4misc.cpp b/tests/auto/qml/v4misc/tst_v4misc.cpp
index 55a1f65608..22ff9c43fc 100644
--- a/tests/auto/qml/v4misc/tst_v4misc.cpp
+++ b/tests/auto/qml/v4misc/tst_v4misc.cpp
@@ -26,207 +26,82 @@
 **
 ****************************************************************************/
 
-#include <qhashfunctions.h>
 #include <qtest.h>
-
-#define V4_AUTOTEST
-#include <private/qv4ssa_p.h>
+#include <private/qv4instr_moth_p.h>
+#include <private/qv4script_p.h>
 
 class tst_v4misc: public QObject
 {
     Q_OBJECT
 
 private slots:
-    void initTestCase();
-
-    void rangeSplitting_1();
-    void rangeSplitting_2();
-    void rangeSplitting_3();
-
-    void moveMapping_1();
-    void moveMapping_2();
+    void tdzOptimizations_data();
+    void tdzOptimizations();
 };
 
-using namespace QT_PREPEND_NAMESPACE(QV4::IR);
-
-void tst_v4misc::initTestCase()
-{
-    qSetGlobalQHashSeed(0);
-    QCOMPARE(qGlobalQHashSeed(), 0);
-}
-
-// split between two ranges
-void tst_v4misc::rangeSplitting_1()
+void tst_v4misc::tdzOptimizations_data()
 {
-    LifeTimeInterval interval;
-    interval.addRange(59, 59);
-    interval.addRange(61, 62);
-    interval.addRange(64, 64);
-    interval.addRange(69, 71);
-    interval.validate();
-    QCOMPARE(interval.end(), 71);
-
-    LifeTimeInterval newInterval = interval.split(66, 70);
-    interval.validate();
-    newInterval.validate();
-    QVERIFY(newInterval.isSplitFromInterval());
-
-    QCOMPARE(interval.ranges().size(), 3);
-    QCOMPARE(interval.ranges()[0].start, 59);
-    QCOMPARE(interval.ranges()[0].end, 59);
-    QCOMPARE(interval.ranges()[1].start, 61);
-    QCOMPARE(interval.ranges()[1].end, 62);
-    QCOMPARE(interval.ranges()[2].start, 64);
-    QCOMPARE(interval.ranges()[2].end, 64);
-    QCOMPARE(interval.end(), 70);
-
-    QCOMPARE(newInterval.ranges().size(), 1);
-    QCOMPARE(newInterval.ranges()[0].start, 70);
-    QCOMPARE(newInterval.ranges()[0].end, 71);
-    QCOMPARE(newInterval.end(), 71);
-}
+    QTest::addColumn<QString>("scriptToCompile");
 
-// split in the middle of a range
-void tst_v4misc::rangeSplitting_2()
-{
-    LifeTimeInterval interval;
-    interval.addRange(59, 59);
-    interval.addRange(61, 64);
-    interval.addRange(69, 71);
-    interval.validate();
-    QCOMPARE(interval.end(), 71);
-
-    LifeTimeInterval newInterval = interval.split(62, 64);
-    interval.validate();
-    newInterval.validate();
-    QVERIFY(newInterval.isSplitFromInterval());
-
-    QCOMPARE(interval.ranges().size(), 2);
-    QCOMPARE(interval.ranges()[0].start, 59);
-    QCOMPARE(interval.ranges()[0].end, 59);
-    QCOMPARE(interval.ranges()[1].start, 61);
-    QCOMPARE(interval.ranges()[1].end, 62);
-    QCOMPARE(interval.end(), 64);
-
-    QCOMPARE(newInterval.ranges().size(), 2);
-    QCOMPARE(newInterval.ranges()[0].start, 64);
-    QCOMPARE(newInterval.ranges()[0].end, 64);
-    QCOMPARE(newInterval.ranges()[1].start, 69);
-    QCOMPARE(newInterval.ranges()[1].end, 71);
-    QCOMPARE(newInterval.end(), 71);
+    QTest::newRow("access-after-let") << QString("let x; x = 10;");
+    QTest::newRow("access-after-const") << QString("const x = 10; print(x);");
+    QTest::newRow("access-after-let") << QString("for (let x of y) print(x);");
 }
 
-// split in the middle of a range, and let it never go back to active again
-void tst_v4misc::rangeSplitting_3()
+void tst_v4misc::tdzOptimizations()
 {
-    LifeTimeInterval interval;
-    interval.addRange(59, 59);
-    interval.addRange(61, 64);
-    interval.addRange(69, 71);
-    interval.validate();
-    QCOMPARE(interval.end(), 71);
-
-    LifeTimeInterval newInterval = interval.split(64, LifeTimeInterval::InvalidPosition);
-    interval.validate();
-    newInterval.validate();
-    QVERIFY(!newInterval.isValid());
-
-    QCOMPARE(interval.ranges().size(), 2);
-    QCOMPARE(interval.ranges()[0].start, 59);
-    QCOMPARE(interval.ranges()[0].end, 59);
-    QCOMPARE(interval.ranges()[1].start, 61);
-    QCOMPARE(interval.ranges()[1].end, 64);
-    QCOMPARE(interval.end(), 71);
-}
+    QFETCH(QString, scriptToCompile);
+
+    QV4::ExecutionEngine v4;
+    QV4::Script script(&v4, nullptr, scriptToCompile);
+    script.parse();
+    QVERIFY(!v4.hasException);
+
+    const auto function = script.compilationUnit->unitData()->functionAt(0);
+    const auto *code = function->code();
+    const auto len = function->codeSize;
+    const char *end = code + len;
+
+    const auto decodeInstruction = [&code]() {
+        QV4::Moth::Instr::Type type = QV4::Moth::Instr::Type(static_cast<uchar>(*code));
+    dispatch:
+        switch (type) {
+            case QV4::Moth::Instr::Type::Nop:
+                ++code;
+                type = QV4::Moth::Instr::Type(static_cast<uchar>(*code));
+                goto dispatch;
+            case QV4::Moth::Instr::Type::Nop_Wide: /* wide prefix */
+                ++code;
+                type = QV4::Moth::Instr::Type(0x100 | static_cast<uchar>(*code));
+                goto dispatch;
+
+#define CASE_AND_GOTO_INSTRUCTION(name, nargs, ...) \
+      case QV4::Moth::Instr::Type::name: \
+            MOTH_ADJUST_CODE(qint8, nargs); \
+            break;
+
+#define CASE_AND_GOTO_WIDE_INSTRUCTION(name, nargs, ...) \
+      case QV4::Moth::Instr::Type::name##_Wide: \
+            MOTH_ADJUST_CODE(int, nargs); \
+            type = QV4::Moth::Instr::Type::name; \
+            break;
+
+#define MOTH_DECODE_WITHOUT_ARGS(instr) \
+     INSTR_##instr(CASE_AND_GOTO) \
+     INSTR_##instr(CASE_AND_GOTO_WIDE)
+
+            FOR_EACH_MOTH_INSTR(MOTH_DECODE_WITHOUT_ARGS)
+        }
+        return type;
+    };
+
+    while (code < end) {
+        QV4::Moth::Instr::Type type = decodeInstruction();
+        QVERIFY(type != QV4::Moth::Instr::Type::DeadTemporalZoneCheck);
+    }
 
-void tst_v4misc::moveMapping_1()
-{
-    Temp fp2(DoubleType, Temp::PhysicalRegister, 2);
-    Temp fp3(DoubleType, Temp::PhysicalRegister, 3);
-    Temp fp4(DoubleType, Temp::PhysicalRegister, 4);
-    Temp fp5(DoubleType, Temp::PhysicalRegister, 5);
-
-    MoveMapping mapping;
-    mapping.add(&fp2, &fp3);
-    mapping.add(&fp2, &fp4);
-    mapping.add(&fp2, &fp5);
-    mapping.add(&fp3, &fp2);
-
-    mapping.order();
-//    mapping.dump();
-
-    QCOMPARE(mapping._moves.size(), 3);
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp2, &fp4, false)));
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp2, &fp5, false)));
-    QVERIFY(mapping._moves.last() == MoveMapping::Move(&fp2, &fp3, true) ||
-            mapping._moves.last() == MoveMapping::Move(&fp3, &fp2, true));
-}
-
-void tst_v4misc::moveMapping_2()
-{
-    Temp fp1(DoubleType, Temp::PhysicalRegister, 1);
-    Temp fp2(DoubleType, Temp::PhysicalRegister, 2);
-    Temp fp3(DoubleType, Temp::PhysicalRegister, 3);
-    Temp fp4(DoubleType, Temp::PhysicalRegister, 4);
-    Temp fp5(DoubleType, Temp::PhysicalRegister, 5);
-    Temp fp6(DoubleType, Temp::PhysicalRegister, 6);
-    Temp fp7(DoubleType, Temp::PhysicalRegister, 7);
-    Temp fp8(DoubleType, Temp::PhysicalRegister, 8);
-    Temp fp9(DoubleType, Temp::PhysicalRegister, 9);
-    Temp fp10(DoubleType, Temp::PhysicalRegister, 10);
-    Temp fp11(DoubleType, Temp::PhysicalRegister, 11);
-    Temp fp12(DoubleType, Temp::PhysicalRegister, 12);
-    Temp fp13(DoubleType, Temp::PhysicalRegister, 13);
-
-    MoveMapping mapping;
-    mapping.add(&fp2, &fp1);
-    mapping.add(&fp2, &fp3);
-    mapping.add(&fp3, &fp2);
-    mapping.add(&fp3, &fp4);
-
-    mapping.add(&fp9, &fp8);
-    mapping.add(&fp8, &fp7);
-    mapping.add(&fp7, &fp6);
-    mapping.add(&fp7, &fp5);
-
-    mapping.add(&fp10, &fp11);
-    mapping.add(&fp11, &fp12);
-    mapping.add(&fp12, &fp13);
-    mapping.add(&fp13, &fp10);
-
-    mapping.order();
-//    mapping.dump();
-
-    QCOMPARE(mapping._moves.size(), 10);
-
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp2, &fp1, false)));
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp3, &fp4, false)));
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp7, &fp6, false)));
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp7, &fp5, false)));
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp8, &fp7, false)));
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp9, &fp8, false)));
-
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp2, &fp3, true)) ||
-            mapping._moves.contains(MoveMapping::Move(&fp3, &fp2, true)));
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp10, &fp13, true)) ||
-            mapping._moves.contains(MoveMapping::Move(&fp13, &fp10, true)));
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp12, &fp13, true)) ||
-            mapping._moves.contains(MoveMapping::Move(&fp13, &fp12, true)));
-    QVERIFY(mapping._moves.contains(MoveMapping::Move(&fp12, &fp11, true)) ||
-            mapping._moves.contains(MoveMapping::Move(&fp11, &fp12, true)));
-
-    QVERIFY(!mapping._moves.at(0).needsSwap);
-    QVERIFY(!mapping._moves.at(1).needsSwap);
-    QVERIFY(!mapping._moves.at(2).needsSwap);
-    QVERIFY(!mapping._moves.at(3).needsSwap);
-    QVERIFY(!mapping._moves.at(4).needsSwap);
-    QVERIFY(!mapping._moves.at(5).needsSwap);
-    QVERIFY(mapping._moves.at(6).needsSwap);
-    QVERIFY(mapping._moves.at(7).needsSwap);
-    QVERIFY(mapping._moves.at(8).needsSwap);
-    QVERIFY(mapping._moves.at(9).needsSwap);
 }
 
-QTEST_MAIN(tst_v4misc)
+QTEST_MAIN(tst_v4misc);
 
 #include "tst_v4misc.moc"