Remove invalid QJSValue type

Rationale: It's confusing to have an invalid type (which doesn't
exist in JavaScript), and it creates lots of extra cases that have
to be handled e.g. in value conversion and comparison. The Undefined
type should be sufficient.

Also, the invalid value type was being (ab)used to 1) make
setProperty() act as a property deleter, and 2) signify that a
property queried by property() doesn't exist. The recently introduced
functions has(Own)Property() and deleteProperty() now provide that
functionality.

Default-constructed QJSValues now have the Undefined type.

Task-number: QTBUG-23604
Change-Id: I1847492724d31e03ee1212c09ec87a2010920dc5
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@nokia.com>

10 files changed, 191 insertions, 347 deletions

diff --git a/src/declarative/qml/v8/qjsvalue.cpp b/src/declarative/qml/v8/qjsvalue.cpp
index a34031d555..73b7e4f9c7 100644
--- a/src/declarative/qml/v8/qjsvalue.cpp
+++ b/src/declarative/qml/v8/qjsvalue.cpp
@@ -111,14 +111,6 @@
 QT_BEGIN_NAMESPACE
 
 /*!
-    Constructs an invalid value.
-*/
-QJSValue::QJSValue()
-    : d_ptr(InvalidValue())
-{
-}
-
-/*!
   Constructs a new QJSValue with a boolean \a value.
 */
 QJSValue::QJSValue(bool value)
@@ -347,23 +339,6 @@ QJSValue::~QJSValue()
 {
 }
 
-#ifdef QT_DEPRECATED
-
-/*!
-  \obsolete
-
-  Returns true if this QJSValue is valid; otherwise returns
-  false.
-*/
-bool QJSValue::isValid() const
-{
-    Q_D(const QJSValue);
-    QScriptIsolate api(d->engine());
-    return d->isValid();
-}
-
-#endif // QT_DEPRECATED
-
 /*!
   Returns true if this QJSValue is of the primitive type Boolean;
   otherwise returns false.
@@ -693,7 +668,7 @@ QJSValue QJSValue::call(const QJSValueList &args)
   the function.
 
   If this QJSValue is not a function, call() does nothing
-  and returns an invalid QJSValue.
+  and returns an undefined QJSValue.
 
   Note that if \a instance is not an object, the global object
   (see \l{QJSEngine::globalObject()}) will be used as the
@@ -787,7 +762,7 @@ QJSEngine* QJSValue::engine() const
 /*!
   If this QJSValue is an object, returns the internal prototype
   (\c{__proto__} property) of this object; otherwise returns an
-  invalid QJSValue.
+  undefined QJSValue.
 
   \sa setPrototype(), isObject()
 */
@@ -893,7 +868,7 @@ bool QJSValue::strictlyEquals(const QJSValue& other) const
 
 /*!
   Returns the value of this QJSValue's property with the given \a name.
-  If no such property exists, an invalid QJSValue is returned.
+  If no such property exists, an undefined QJSValue is returned.
 
   If the property is implemented using a getter function (i.e. has the
   PropertyGetter flag set), calling property() has side-effects on the
@@ -939,18 +914,6 @@ QJSValue QJSValue::property(quint32 arrayIndex) const
   If this QJSValue does not already have a property with name \a name,
   a new property is created.
 
-  If \a value is invalid, the property is removed.
-
-  If the property is implemented using a setter function (i.e. has the
-  PropertySetter flag set), calling setProperty() has side-effects on
-  the script engine, since the setter function will be called with the
-  given \a value as argument (possibly resulting in an uncaught script
-  exception).
-
-  Note that you cannot specify custom getter or setter functions for
-  built-in properties, such as the \c{length} property of Array objects
-  or meta properties of QObject objects.
-
   \sa property(), deleteProperty()
 */
 void QJSValue::setProperty(const QString& name, const QJSValue& value)
diff --git a/src/declarative/qml/v8/qjsvalue.h b/src/declarative/qml/v8/qjsvalue.h
index f0be07e725..8ec2932dc3 100644
--- a/src/declarative/qml/v8/qjsvalue.h
+++ b/src/declarative/qml/v8/qjsvalue.h
@@ -66,11 +66,10 @@ public:
     };
 
 public:
-    QJSValue();
+    QJSValue(SpecialValue value = UndefinedValue);
     ~QJSValue();
     QJSValue(const QJSValue &other);
 
-    QJSValue(SpecialValue value);
     QJSValue(bool value);
     QJSValue(int value);
     QJSValue(uint value);
@@ -137,7 +136,6 @@ public:
 
     QT_DEPRECATED QJSEngine *engine() const;
 
-    QT_DEPRECATED bool isValid() const;
     QT_DEPRECATED bool isFunction() const;
     QT_DEPRECATED qint32 toInt32() const;
     QT_DEPRECATED quint32 toUInt32() const;
diff --git a/src/declarative/qml/v8/qjsvalue_impl_p.h b/src/declarative/qml/v8/qjsvalue_impl_p.h
index 386b203a41..b4e66ed093 100644
--- a/src/declarative/qml/v8/qjsvalue_impl_p.h
+++ b/src/declarative/qml/v8/qjsvalue_impl_p.h
@@ -42,30 +42,6 @@
 
 QT_BEGIN_NAMESPACE
 
-// This template is used indirectly by the Q_GLOBAL_STATIC macro below
-template<>
-class QGlobalStaticDeleter<QJSValuePrivate>
-{
-public:
-    QGlobalStatic<QJSValuePrivate> &globalStatic;
-    QGlobalStaticDeleter(QGlobalStatic<QJSValuePrivate> &_globalStatic)
-        : globalStatic(_globalStatic)
-    {
-        globalStatic.pointer.load()->ref.ref();
-    }
-
-    inline ~QGlobalStaticDeleter()
-    {
-        if (!globalStatic.pointer.load()->ref.deref()) { // Logic copy & paste from SharedDataPointer
-            delete globalStatic.pointer.load();
-        }
-        globalStatic.pointer.store(0);
-        globalStatic.destroyed = true;
-    }
-};
-
-Q_GLOBAL_STATIC(QJSValuePrivate, InvalidValue)
-
 QJSValuePrivate* QJSValuePrivate::get(const QJSValue& q) { Q_ASSERT(q.d_ptr.data()); return q.d_ptr.data(); }
 
 QJSValue QJSValuePrivate::get(const QJSValuePrivate* d)
@@ -86,11 +62,6 @@ QJSValue QJSValuePrivate::get(QJSValuePrivate* d)
     return QJSValue(d);
 }
 
-QJSValuePrivate::QJSValuePrivate()
-    : m_engine(0), m_state(Invalid)
-{
-}
-
 QJSValuePrivate::QJSValuePrivate(bool value)
     : m_engine(0), m_state(CBool), u(value)
 {
@@ -208,7 +179,6 @@ bool QJSValuePrivate::toBool() const
         return !(qIsNaN(u.m_number) || !u.m_number);
     case CBool:
         return u.m_bool;
-    case Invalid:
     case CNull:
     case CUndefined:
         return false;
@@ -233,8 +203,6 @@ double QJSValuePrivate::toNumber() const
     case CBool:
         return u.m_bool ? 1 : 0;
     case CNull:
-    case Invalid:
-        return 0;
     case CUndefined:
         return qQNaN();
     case CString:
@@ -259,8 +227,6 @@ double QJSValuePrivate::toNumber() const
 QString QJSValuePrivate::toString() const
 {
     switch (m_state) {
-    case Invalid:
-        return QString();
     case CBool:
         return u.m_bool ? QString::fromLatin1("true") : QString::fromLatin1("false");
     case CString:
@@ -290,8 +256,6 @@ QString QJSValuePrivate::toString() const
 QVariant QJSValuePrivate::toVariant() const
 {
     switch (m_state) {
-        case Invalid:
-            return QVariant();
         case CBool:
             return QVariant(u.m_bool);
         case CString:
@@ -427,11 +391,6 @@ inline bool QJSValuePrivate::isUndefined() const
     return m_state == CUndefined || (isJSBased() && m_value->IsUndefined());
 }
 
-inline bool QJSValuePrivate::isValid() const
-{
-    return m_state != Invalid;
-}
-
 inline bool QJSValuePrivate::isVariant() const
 {
     return isJSBased() && m_engine->isVariant(m_value);
@@ -454,12 +413,6 @@ bool QJSValuePrivate::isQObject() const
 
 inline bool QJSValuePrivate::equals(QJSValuePrivate* other)
 {
-    if (!isValid())
-        return !other->isValid();
-
-    if (!other->isValid())
-        return false;
-
     if (!isJSBased() && !other->isJSBased()) {
         switch (m_state) {
         case CNull:
@@ -559,10 +512,8 @@ inline bool QJSValuePrivate::strictlyEquals(QJSValuePrivate* other)
         return u.m_bool == other->u.m_bool;
     }
 
-    if (!isValid() && !other->isValid())
-        return true;
-
-    return false;
+    return (isUndefined() && other->isUndefined())
+            || (isNull() && other->isNull());
 }
 
 inline bool QJSValuePrivate::lessThan(QJSValuePrivate *other) const
@@ -572,9 +523,6 @@ inline bool QJSValuePrivate::lessThan(QJSValuePrivate *other) const
         return false;
     }
 
-    if (!isValid() || !other->isValid())
-        return false;
-
     if (isString() && other->isString())
         return toString() < other->toString();
 
@@ -609,7 +557,7 @@ inline QScriptPassPointer<QJSValuePrivate> QJSValuePrivate::prototype() const
         v8::HandleScope handleScope;
         return new QJSValuePrivate(engine(), v8::Handle<v8::Object>::Cast(m_value)->GetPrototype());
     }
-    return InvalidValue();
+    return new QJSValuePrivate();
 }
 
 inline void QJSValuePrivate::setPrototype(QJSValuePrivate* prototype)
@@ -644,42 +592,6 @@ inline void QJSValuePrivate::setProperty(v8::Handle<v8::String> name, QJSValuePr
     if (!value->isJSBased())
         value->assignEngine(engine());
 
-    if (!value->isValid()) {
-        // Remove the property.
-        v8::HandleScope handleScope;
-        v8::TryCatch tryCatch;
-        v8::Handle<v8::Object> recv(v8::Object::Cast(*m_value));
-//        if (attribs & QJSValue::PropertyGetter && !(attribs & QJSValue::PropertySetter)) {
-//            v8::Local<v8::Object> descriptor = engine()->originalGlobalObject()->getOwnPropertyDescriptor(recv, name);
-//            if (!descriptor.IsEmpty()) {
-//                v8::Local<v8::Value> setter = descriptor->Get(v8::String::New("set"));
-//                if (!setter.IsEmpty() && !setter->IsUndefined()) {
-//                    recv->Delete(name);
-//                    engine()->originalGlobalObject()->defineGetterOrSetter(recv, name, setter, QJSValue::PropertySetter);
-//                    if (tryCatch.HasCaught())
-//                        engine()->setException(tryCatch.Exception(), tryCatch.Message());
-//                    return;
-//                }
-//            }
-//        } else if (attribs & QJSValue::PropertySetter && !(attribs & QJSValue::PropertyGetter)) {
-//            v8::Local<v8::Object> descriptor = engine()->originalGlobalObject()->getOwnPropertyDescriptor(recv, name);
-//            if (!descriptor.IsEmpty()) {
-//                v8::Local<v8::Value> getter = descriptor->Get(v8::String::New("get"));
-//                if (!getter.IsEmpty() && !getter->IsUndefined()) {
-//                    recv->Delete(name);
-//                    engine()->originalGlobalObject()->defineGetterOrSetter(recv, name, getter, QJSValue::PropertyGetter);
-//                    if (tryCatch.HasCaught())
-//                        engine()->setException(tryCatch.Exception(), tryCatch.Message());
-//                    return;
-//                }
-//            }
-//        }
-        recv->Delete(name);
-        if (tryCatch.HasCaught())
-            engine()->setException(tryCatch.Exception(), tryCatch.Message());
-        return;
-    }
-
     if (engine() != value->engine()) {
         qWarning("QJSValue::setProperty(%s) failed: "
                  "cannot set value created in a different engine",
@@ -715,16 +627,6 @@ inline void QJSValuePrivate::setProperty(quint32 index, QJSValuePrivate* value,
     if (!value->isJSBased())
         value->assignEngine(engine());
 
-    if (!value->isValid()) {
-        // Remove the property.
-        v8::HandleScope handleScope;
-        v8::TryCatch tryCatch;
-        v8::Object::Cast(*m_value)->Delete(index);
-        if (tryCatch.HasCaught())
-            engine()->setException(tryCatch.Exception(), tryCatch.Message());
-        return;
-    }
-
     if (engine() != value->engine()) {
         qWarning("QJSValue::setProperty() failed: cannot set value created in a different engine");
         return;
@@ -739,10 +641,10 @@ inline void QJSValuePrivate::setProperty(quint32 index, QJSValuePrivate* value,
 
 inline QScriptPassPointer<QJSValuePrivate> QJSValuePrivate::property(const QString& name) const
 {
-    if (!name.length())
-        return InvalidValue();
     if (!isObject())
-        return InvalidValue();
+        return new QJSValuePrivate();
+    if (!name.length())
+        return new QJSValuePrivate(engine());
 
     v8::HandleScope handleScope;
     return property(QJSConverter::toString(name));
@@ -752,14 +654,14 @@ inline QScriptPassPointer<QJSValuePrivate> QJSValuePrivate::property(v8::Handle<
 {
     Q_ASSERT(!name.IsEmpty());
     if (!isObject())
-        return InvalidValue();
+        return new QJSValuePrivate();
     return property<>(name);
 }
 
 inline QScriptPassPointer<QJSValuePrivate> QJSValuePrivate::property(quint32 index) const
 {
     if (!isObject())
-        return InvalidValue();
+        return new QJSValuePrivate();
     return property<>(index);
 }
 
@@ -777,11 +679,8 @@ inline QScriptPassPointer<QJSValuePrivate> QJSValuePrivate::property(T name) con
         engine()->setException(result, tryCatch.Message());
         return new QJSValuePrivate(engine(), result);
     }
-    if (result.IsEmpty() || (result->IsUndefined() && !self->Has(name))) {
-        // In QtScript we make a distinction between a property that exists and has value undefined,
-        // and a property that doesn't exist; in the latter case, we should return an invalid value.
-        return InvalidValue();
-    }
+    if (result.IsEmpty())
+        return new QJSValuePrivate(engine());
     return new QJSValuePrivate(engine(), result);
 }
 
@@ -836,7 +735,7 @@ inline QJSValue::PropertyFlags QJSValuePrivate::propertyFlags(v8::Handle<v8::Str
 inline QScriptPassPointer<QJSValuePrivate> QJSValuePrivate::call(QJSValuePrivate* thisObject, const QJSValueList& args)
 {
     if (!isCallable())
-        return InvalidValue();
+        return new QJSValuePrivate();
 
     v8::HandleScope handleScope;
 
@@ -845,7 +744,7 @@ inline QScriptPassPointer<QJSValuePrivate> QJSValuePrivate::call(QJSValuePrivate
     QVarLengthArray<v8::Handle<v8::Value>, 8> argv(argc);
     if (!prepareArgumentsForCall(argv.data(), args)) {
         qWarning("QJSValue::call() failed: cannot call function with argument created in a different engine");
-        return InvalidValue();
+        return new QJSValuePrivate(engine());
     }
 
     return call(thisObject, argc, argv.data());
@@ -862,7 +761,7 @@ QScriptPassPointer<QJSValuePrivate> QJSValuePrivate::call(QJSValuePrivate* thisO
     } else {
         if (!thisObject->assignEngine(e)) {
             qWarning("QJSValue::call() failed: cannot call function with thisObject created in a different engine");
-            return InvalidValue();
+            return new QJSValuePrivate(engine());
         }
 
         recv = v8::Handle<v8::Object>(v8::Object::Cast(*thisObject->m_value));
@@ -913,7 +812,7 @@ inline QScriptPassPointer<QJSValuePrivate> QJSValuePrivate::callAsConstructor(in
 inline QScriptPassPointer<QJSValuePrivate> QJSValuePrivate::callAsConstructor(const QJSValueList& args)
 {
     if (!isCallable())
-        return InvalidValue();
+        return new QJSValuePrivate();
 
     v8::HandleScope handleScope;
 
@@ -922,23 +821,21 @@ inline QScriptPassPointer<QJSValuePrivate> QJSValuePrivate::callAsConstructor(co
     QVarLengthArray<v8::Handle<v8::Value>, 8> argv(argc);
     if (!prepareArgumentsForCall(argv.data(), args)) {
         qWarning("QJSValue::callAsConstructor() failed: cannot construct function with argument created in a different engine");
-        return InvalidValue();
+        return new QJSValuePrivate(engine());
     }
 
     return callAsConstructor(argc, argv.data());
 }
 
 /*! \internal
- * Make sure this value is associated with a v8 value belogning to this engine.
- * If the value was invalid, or belogning to another engine, return false.
+ * Make sure this value is associated with a v8 value belonging to this engine.
+ * If the value belongs to another engine, returns false.
  */
 bool QJSValuePrivate::assignEngine(QV8Engine* engine)
 {
     Q_ASSERT(engine);
     v8::HandleScope handleScope;
     switch (m_state) {
-    case Invalid:
-        return false;
     case CBool:
         m_value = v8::Persistent<v8::Value>::New(engine->makeJSValue(u.m_bool));
         break;
@@ -973,7 +870,7 @@ bool QJSValuePrivate::assignEngine(QV8Engine* engine)
 
 /*!
   \internal
-  Invalidates this value.
+  Invalidates this value (makes it undefined).
 
   Does not remove the value from the engine's list of
   registered values; that's the responsibility of the caller.
@@ -987,7 +884,7 @@ void QJSValuePrivate::invalidate()
         delete u.m_string;
     }
     m_engine = 0;
-    m_state = Invalid;
+    m_state = CUndefined;
 }
 
 QV8Engine* QJSValuePrivate::engine() const
@@ -1059,13 +956,10 @@ inline bool QJSValuePrivate::prepareArgumentsForCall(v8::Handle<v8::Value> argv[
     for (int j = 0; i != args.constEnd(); j++, i++) {
         QJSValuePrivate* value = QJSValuePrivate::get(*i);
         if ((value->isJSBased() && engine() != value->engine())
-                || (!value->isJSBased() && value->isValid() && !value->assignEngine(engine())))
+                || (!value->isJSBased() && !value->assignEngine(engine())))
             // Different engines are not allowed!
             return false;
-        if (value->isValid())
-            argv[j] = *value;
-        else
-            argv[j] = engine()->makeJSValue(QJSValue::UndefinedValue);
+        argv[j] = *value;
     }
     return true;
 }
diff --git a/src/declarative/qml/v8/qjsvalue_p.h b/src/declarative/qml/v8/qjsvalue_p.h
index fd32a14bb8..02ffc8108e 100644
--- a/src/declarative/qml/v8/qjsvalue_p.h
+++ b/src/declarative/qml/v8/qjsvalue_p.h
@@ -59,7 +59,6 @@ class QJSValuePrivate
         : public QSharedData
 {
 public:
-    inline QJSValuePrivate();
     inline static QJSValuePrivate* get(const QJSValue& q);
     inline static QJSValue get(const QJSValuePrivate* d);
     inline static QJSValue get(QJSValuePrivate* d);
@@ -71,14 +70,14 @@ public:
     inline QJSValuePrivate(uint value);
     inline QJSValuePrivate(double value);
     inline QJSValuePrivate(const QString& value);
-    inline QJSValuePrivate(QJSValue::SpecialValue value);
+    inline QJSValuePrivate(QJSValue::SpecialValue value = QJSValue::UndefinedValue);
 
     inline QJSValuePrivate(QV8Engine *engine, bool value);
     inline QJSValuePrivate(QV8Engine *engine, int value);
     inline QJSValuePrivate(QV8Engine *engine, uint value);
     inline QJSValuePrivate(QV8Engine *engine, double value);
     inline QJSValuePrivate(QV8Engine *engine, const QString& value);
-    inline QJSValuePrivate(QV8Engine *engine, QJSValue::SpecialValue value);
+    inline QJSValuePrivate(QV8Engine *engine, QJSValue::SpecialValue value = QJSValue::UndefinedValue);
     inline QJSValuePrivate(QV8Engine *engine, v8::Handle<v8::Value>);
     inline void invalidate();
 
@@ -103,7 +102,6 @@ public:
     inline bool isObject() const;
     inline bool isString() const;
     inline bool isUndefined() const;
-    inline bool isValid() const;
     inline bool isVariant() const;
     inline bool isDate() const;
     inline bool isRegExp() const;
@@ -149,7 +147,6 @@ private:
 
     // Please, update class documentation when you change the enum.
     enum State {
-        Invalid = 0,
         CString = 0x1000,
         CNumber,
         CBool,
diff --git a/src/declarative/qml/v8/qjsvalueiterator_impl_p.h b/src/declarative/qml/v8/qjsvalueiterator_impl_p.h
index e287bc175c..40814b1969 100644
--- a/src/declarative/qml/v8/qjsvalueiterator_impl_p.h
+++ b/src/declarative/qml/v8/qjsvalueiterator_impl_p.h
@@ -97,7 +97,7 @@ inline QString QJSValueIteratorPrivate::name() const
 inline QScriptPassPointer<QJSValuePrivate> QJSValueIteratorPrivate::value() const
 {
     if (!isValid())
-        return InvalidValue();
+        return new QJSValuePrivate();
 
     v8::HandleScope handleScope;
     return m_object->property(m_names->Get(m_index - 1)->ToString());
@@ -105,7 +105,7 @@ inline QScriptPassPointer<QJSValuePrivate> QJSValueIteratorPrivate::value() cons
 
 inline bool QJSValueIteratorPrivate::isValid() const
 {
-    bool result = m_object ? m_object->isValid() : false;
+    bool result = m_object ? !m_object->isUndefined() : false;
     // We know that if this object is still valid then it is an object
     // if this assumption is not correct then some other logic in this class
     // have to be changed too.
diff --git a/src/declarative/qml/v8/qv8engine.cpp b/src/declarative/qml/v8/qv8engine.cpp
index 50250ffc8f..2f266a010e 100644
--- a/src/declarative/qml/v8/qv8engine.cpp
+++ b/src/declarative/qml/v8/qv8engine.cpp
@@ -1435,7 +1435,7 @@ QScriptPassPointer<QJSValuePrivate> QV8Engine::evaluate(v8::Handle<v8::Script> s
         v8::Handle<v8::Value> exception = tryCatch.Exception();
         if (exception.IsEmpty()) {
             // This is possible on syntax errors like { a:12, b:21 } <- missing "(", ")" around expression.
-            return InvalidValue();
+            return new QJSValuePrivate(this);
         }
         setException(exception, tryCatch.Message());
         return new QJSValuePrivate(this, exception);
@@ -1457,7 +1457,7 @@ QScriptPassPointer<QJSValuePrivate> QV8Engine::evaluate(v8::Handle<v8::Script> s
 QJSValue QV8Engine::scriptValueFromInternal(v8::Handle<v8::Value> value) const
 {
     if (value.IsEmpty())
-        return QJSValuePrivate::get(InvalidValue());
+        return QJSValuePrivate::get(new QJSValuePrivate(const_cast<QV8Engine*>(this)));
     return QJSValuePrivate::get(new QJSValuePrivate(const_cast<QV8Engine*>(this), value));
 }
 
diff --git a/src/declarative/qml/v8/qv8typewrapper.cpp b/src/declarative/qml/v8/qv8typewrapper.cpp
index 9c362dbea9..0a4c390814 100644
--- a/src/declarative/qml/v8/qv8typewrapper.cpp
+++ b/src/declarative/qml/v8/qv8typewrapper.cpp
@@ -240,7 +240,7 @@ v8::Handle<v8::Value> QV8TypeWrapper::Getter(v8::Local<v8::String> property,
                 // check for property.
                 v8::Handle<v8::Value> rv = v8engine->qobjectWrapper()->getProperty(moduleApi->qobjectApi, propertystring, QV8QObjectWrapper::IgnoreRevision);
                 return rv;
-            } else if (moduleApi->scriptApi.isValid()) {
+            } else if (!moduleApi->scriptApi.isUndefined()) {
                 // NOTE: if used in a binding, changes will not trigger re-evaluation since non-NOTIFYable.
                 QJSValuePrivate *apiprivate = QJSValuePrivate::get(moduleApi->scriptApi);
                 QScopedPointer<QJSValuePrivate> propertyValue(apiprivate->property(property).give());
@@ -294,7 +294,7 @@ v8::Handle<v8::Value> QV8TypeWrapper::Setter(v8::Local<v8::String> property,
             if (moduleApi->qobjectApi) {
                 v8engine->qobjectWrapper()->setProperty(moduleApi->qobjectApi, propertystring, value, 
                                                         QV8QObjectWrapper::IgnoreRevision);
-            } else if (moduleApi->scriptApi.isValid()) {
+            } else if (!moduleApi->scriptApi.isUndefined()) {
                 QScopedPointer<QJSValuePrivate> setvalp(new QJSValuePrivate(v8engine, value));
                 QJSValuePrivate *apiprivate = QJSValuePrivate::get(moduleApi->scriptApi);
                 if (apiprivate->propertyFlags(property) & QJSValue::ReadOnly) {
diff --git a/tests/auto/declarative/qjsengine/tst_qjsengine.cpp b/tests/auto/declarative/qjsengine/tst_qjsengine.cpp
index 2d49619a8c..ca45d7e1c3 100644
--- a/tests/auto/declarative/qjsengine/tst_qjsengine.cpp
+++ b/tests/auto/declarative/qjsengine/tst_qjsengine.cpp
@@ -347,7 +347,7 @@ void tst_QJSEngine::currentContext()
     QCOMPARE(globalCtx->argumentCount(), 0);
     QCOMPARE(globalCtx->backtrace().size(), 1);
     QVERIFY(!globalCtx->isCalledAsConstructor());
-    QVERIFY(!globalCtx->callee().isValid());
+    QVERIFY(globalCtx->callee().isUndefined());
     QCOMPARE(globalCtx->state(), QScriptContext::NormalState);
     QVERIFY(globalCtx->thisObject().strictlyEquals(eng.globalObject()));
     QVERIFY(globalCtx->activationObject().strictlyEquals(eng.globalObject()));
@@ -362,7 +362,7 @@ void tst_QJSEngine::pushPopContext()
     QVERIFY(ctx != 0);
     QCOMPARE(ctx->parentContext(), globalCtx);
     QVERIFY(!ctx->isCalledAsConstructor());
-    QVERIFY(!ctx->callee().isValid());
+    QVERIFY(ctx->callee().isUndefined());
     QVERIFY(ctx->thisObject().strictlyEquals(eng.globalObject()));
     QCOMPARE(ctx->argumentCount(), 0);
     QCOMPARE(ctx->backtrace().size(), 2);
@@ -434,7 +434,7 @@ void tst_QJSEngine::newFunction()
     QScriptEngine eng;
     {
         QScriptValue fun = eng.newFunction(myFunction);
-        QCOMPARE(fun.isValid(), true);
+        QVERIFY(!fun.isUndefined());
         QCOMPARE(fun.isCallable(), true);
         QCOMPARE(fun.isObject(), true);
         QCOMPARE(fun.scriptClass(), (QScriptClass*)0);
@@ -447,7 +447,7 @@ void tst_QJSEngine::newFunction()
             QCOMPARE(prot.propertyFlags("constructor"), QScriptValue::SkipInEnumeration);
         }
         // prototype should be Function.prototype
-        QCOMPARE(fun.prototype().isValid(), true);
+        QVERIFY(!fun.prototype().isUndefined());
         QCOMPARE(fun.prototype().isCallable(), true);
         QCOMPARE(fun.prototype().strictlyEquals(eng.evaluate("Function.prototype")), true);
 
@@ -472,7 +472,7 @@ void tst_QJSEngine::newFunctionWithArg()
             QCOMPARE(prot.propertyFlags("constructor"), QScriptValue::SkipInEnumeration);
         }
         // prototype should be Function.prototype
-        QCOMPARE(fun.prototype().isValid(), true);
+        QVERIFY(!fun.prototype().isUndefined());
         QCOMPARE(fun.prototype().isCallable(), true);
         QCOMPARE(fun.prototype().strictlyEquals(eng.evaluate("Function.prototype")), true);
 
@@ -487,11 +487,11 @@ void tst_QJSEngine::newFunctionWithProto()
     {
         QScriptValue proto = eng.newObject();
         QScriptValue fun = eng.newFunction(myFunction, proto);
-        QCOMPARE(fun.isValid(), true);
+        QVERIFY(!fun.isUndefined());
         QCOMPARE(fun.isCallable(), true);
         QCOMPARE(fun.isObject(), true);
         // internal prototype should be Function.prototype
-        QCOMPARE(fun.prototype().isValid(), true);
+        QVERIFY(!fun.prototype().isUndefined());
         QCOMPARE(fun.prototype().isCallable(), true);
         QCOMPARE(fun.prototype().strictlyEquals(eng.evaluate("Function.prototype")), true);
         // public prototype should be the one we passed
@@ -506,7 +506,7 @@ void tst_QJSEngine::newFunctionWithProto()
     // whether the return value is correct
     {
         QScriptValue fun = eng.newFunction(myFunctionThatReturns);
-        QCOMPARE(fun.isValid(), true);
+        QVERIFY(!fun.isUndefined());
         QCOMPARE(fun.isCallable(), true);
         QCOMPARE(fun.isObject(), true);
 
@@ -517,7 +517,7 @@ void tst_QJSEngine::newFunctionWithProto()
     // whether the return value is assigned to the correct engine
     {
         QScriptValue fun = eng.newFunction(myFunctionThatReturnsWithoutEngine);
-        QCOMPARE(fun.isValid(), true);
+        QVERIFY(!fun.isUndefined());
         QCOMPARE(fun.isCallable(), true);
         QCOMPARE(fun.isObject(), true);
 
@@ -531,13 +531,12 @@ void tst_QJSEngine::newFunctionWithProto()
         QScriptEngine wrongEngine;
 
         QScriptValue fun = eng.newFunction(myFunctionThatReturnsWrongEngine, reinterpret_cast<void *>(&wrongEngine));
-        QCOMPARE(fun.isValid(), true);
+        QVERIFY(!fun.isUndefined());
         QCOMPARE(fun.isCallable(), true);
         QCOMPARE(fun.isObject(), true);
 
         QTest::ignoreMessage(QtWarningMsg, "QScriptValue::call(): Value from different engine returned from native function, returning undefined value instead.");
         QScriptValue result = fun.call();
-        QCOMPARE(result.isValid(), true);
         QCOMPARE(result.isUndefined(), true);
     }
     // checking if arguments are passed correctly
@@ -545,7 +544,7 @@ void tst_QJSEngine::newFunctionWithProto()
         QScriptEngine wrongEngine;
 
         QScriptValue fun = eng.newFunction(sumFunction);
-        QCOMPARE(fun.isValid(), true);
+        QVERIFY(!fun.isUndefined());
         QCOMPARE(fun.isCallable(), true);
         QCOMPARE(fun.isObject(), true);
 
@@ -572,12 +571,12 @@ void tst_QJSEngine::newObject()
 {
     QJSEngine eng;
     QJSValue object = eng.newObject();
-    QCOMPARE(object.isValid(), true);
+    QVERIFY(!object.isUndefined());
     QCOMPARE(object.isObject(), true);
     QCOMPARE(object.isCallable(), false);
 // ###FIXME: No QScriptClass    QCOMPARE(object.scriptClass(), (QScriptClass*)0);
     // prototype should be Object.prototype
-    QCOMPARE(object.prototype().isValid(), true);
+    QVERIFY(!object.prototype().isUndefined());
     QCOMPARE(object.prototype().isObject(), true);
     QCOMPARE(object.prototype().strictlyEquals(eng.evaluate("Object.prototype")), true);
 }
@@ -586,13 +585,13 @@ void tst_QJSEngine::newArray()
 {
     QJSEngine eng;
     QJSValue array = eng.newArray();
-    QCOMPARE(array.isValid(), true);
+    QVERIFY(!array.isUndefined());
     QCOMPARE(array.isArray(), true);
     QCOMPARE(array.isObject(), true);
     QVERIFY(!array.isCallable());
 // ###FIXME: No QScriptClass    QCOMPARE(array.scriptClass(), (QScriptClass*)0);
     // prototype should be Array.prototype
-    QCOMPARE(array.prototype().isValid(), true);
+    QVERIFY(!array.prototype().isUndefined());
     QCOMPARE(array.prototype().isArray(), true);
     QCOMPARE(array.prototype().strictlyEquals(eng.evaluate("Array.prototype")), true);
 }
@@ -655,11 +654,11 @@ void tst_QJSEngine::newVariant()
     QJSEngine eng;
     {
         QJSValue opaque = eng.toScriptValue(QVariant(QPoint(1, 2)));
-        QCOMPARE(opaque.isValid(), true);
+        QVERIFY(!opaque.isUndefined());
         QCOMPARE(opaque.isVariant(), true);
         QVERIFY(!opaque.isCallable());
         QCOMPARE(opaque.isObject(), true);
-        QCOMPARE(opaque.prototype().isValid(), true);
+        QVERIFY(!opaque.prototype().isUndefined());
         QEXPECT_FAIL("", "FIXME: newly created QObject's prototype is an JS Object", Continue);
         QCOMPARE(opaque.prototype().isVariant(), true);
         QVERIFY(opaque.property("valueOf").callWithInstance(opaque).equals(opaque));
@@ -700,7 +699,7 @@ void tst_QJSEngine::newVariant_promoteObject()
         QScriptValue originalProto = object.property("foo").prototype();
         QSKIP("It is not possible to promote plain object to a wrapper");
         QScriptValue ret = eng.newVariant(object.property("foo"), QVariant(123));
-        QVERIFY(ret.isValid());
+        QVERIFY(ret.isObject());
         QVERIFY(ret.strictlyEquals(object.property("foo")));
         QVERIFY(ret.isVariant());
         QVERIFY(object.property("foo").isVariant());
@@ -718,7 +717,7 @@ void tst_QJSEngine::newVariant_replaceValue()
         QScriptValue object = eng.newVariant(QVariant(123));
         for (int x = 0; x < 2; ++x) {
             QScriptValue ret = eng.newVariant(object, QVariant(456));
-            QVERIFY(ret.isValid());
+            QVERIFY(!ret.isUndefined());
             QVERIFY(ret.strictlyEquals(object));
             QVERIFY(ret.isVariant());
             QCOMPARE(ret.toVariant(), QVariant(456));
@@ -759,7 +758,7 @@ void tst_QJSEngine::newVariant_promoteNonQScriptObject()
     {
         QTest::ignoreMessage(QtWarningMsg, "QScriptEngine::newVariant(): changing class of non-QScriptObject not supported");
         QScriptValue ret = eng.newVariant(eng.newArray(), 123);
-        QVERIFY(!ret.isValid());
+        QVERIFY(ret.isUndefined());
     }
 }
 #endif
@@ -769,12 +768,12 @@ void tst_QJSEngine::newRegExp()
     QSKIP("Test failing - QTBUG-22238");
     QJSEngine eng;
     QJSValue rexp = eng.toScriptValue(QRegExp("foo"));
-    QCOMPARE(rexp.isValid(), true);
+    QVERIFY(!rexp.isUndefined());
     QCOMPARE(rexp.isRegExp(), true);
     QCOMPARE(rexp.isObject(), true);
     QVERIFY(rexp.isCallable()); // in JSC, RegExp objects are callable
     // prototype should be RegExp.prototype
-    QCOMPARE(rexp.prototype().isValid(), true);
+    QVERIFY(!rexp.prototype().isUndefined());
     QCOMPARE(rexp.prototype().isObject(), true);
     QCOMPARE(rexp.prototype().isRegExp(), false);
     QCOMPARE(rexp.prototype().strictlyEquals(eng.evaluate("RegExp.prototype")), true);
@@ -853,12 +852,12 @@ void tst_QJSEngine::newDate()
 
     {
         QJSValue date = eng.evaluate("new Date(0)");
-        QCOMPARE(date.isValid(), true);
+        QVERIFY(!date.isUndefined());
         QCOMPARE(date.isDate(), true);
         QCOMPARE(date.isObject(), true);
         QVERIFY(!date.isCallable());
         // prototype should be Date.prototype
-        QCOMPARE(date.prototype().isValid(), true);
+        QVERIFY(!date.prototype().isUndefined());
         QCOMPARE(date.prototype().isDate(), true);
         QCOMPARE(date.prototype().strictlyEquals(eng.evaluate("Date.prototype")), true);
     }
@@ -866,11 +865,11 @@ void tst_QJSEngine::newDate()
     {
         QDateTime dt = QDateTime(QDate(1, 2, 3), QTime(4, 5, 6, 7), Qt::LocalTime);
         QJSValue date = eng.toScriptValue(dt);
-        QCOMPARE(date.isValid(), true);
+        QVERIFY(!date.isUndefined());
         QCOMPARE(date.isDate(), true);
         QCOMPARE(date.isObject(), true);
         // prototype should be Date.prototype
-        QCOMPARE(date.prototype().isValid(), true);
+        QVERIFY(!date.prototype().isUndefined());
         QCOMPARE(date.prototype().isDate(), true);
         QCOMPARE(date.prototype().strictlyEquals(eng.evaluate("Date.prototype")), true);
 
@@ -909,20 +908,19 @@ void tst_QJSEngine::newQObject()
 
     {
         QJSValue qobject = eng.newQObject(0);
-        QCOMPARE(qobject.isValid(), true);
         QCOMPARE(qobject.isNull(), true);
         QCOMPARE(qobject.isObject(), false);
         QCOMPARE(qobject.toQObject(), (QObject *)0);
     }
     {
         QJSValue qobject = eng.newQObject(this);
-        QCOMPARE(qobject.isValid(), true);
+        QVERIFY(!qobject.isUndefined());
         QCOMPARE(qobject.isQObject(), true);
         QCOMPARE(qobject.isObject(), true);
         QCOMPARE(qobject.toQObject(), (QObject *)this);
         QVERIFY(!qobject.isCallable());
         // prototype should be QObject.prototype
-        QCOMPARE(qobject.prototype().isValid(), true);
+        QCOMPARE(qobject.prototype().isObject(), true);
         QEXPECT_FAIL("", "FIXME: newly created QObject's prototype is an JS Object", Continue);
         QCOMPARE(qobject.prototype().isQObject(), true);
 // ###FIXME: No QScriptClass        QCOMPARE(qobject.scriptClass(), (QScriptClass*)0);
@@ -997,7 +995,7 @@ void tst_QJSEngine::newQObject_promoteObject()
         QScriptValue obj = eng.newObject();
         QScriptValue originalProto = obj.prototype();
         QScriptValue ret = eng.newQObject(obj, this);
-        QVERIFY(ret.isValid());
+        QVERIFY(!ret.isUndefined());
         QVERIFY(ret.isQObject());
         QVERIFY(ret.strictlyEquals(obj));
         QVERIFY(obj.isQObject());
@@ -1025,7 +1023,7 @@ void tst_QJSEngine::newQObject_promoteObject()
         QObject otherQObject;
         for (int x = 0; x < 2; ++x) {
             QScriptValue ret = eng.newQObject(object, &otherQObject);
-            QVERIFY(ret.isValid());
+            QVERIFY(!ret.isUndefined());
             QVERIFY(ret.isQObject());
             QVERIFY(ret.strictlyEquals(object));
             QCOMPARE(ret.toQObject(), (QObject *)&otherQObject);
@@ -1121,7 +1119,7 @@ void tst_QJSEngine::newQObject_promoteNonQScriptObject()
     {
         QTest::ignoreMessage(QtWarningMsg, "QScriptEngine::newQObject(): changing class of non-QScriptObject not supported");
         QScriptValue ret = eng.newQObject(eng.newArray(), this);
-        QVERIFY(!ret.isValid());
+        QVERIFY(ret.isUndefined());
     }
 #endif
 }
@@ -1161,13 +1159,13 @@ void tst_QJSEngine::newQMetaObject()
     QScriptValue qclass = qScriptValueFromQMetaObject<QObject>(&eng);
     QScriptValue qclass2 = qScriptValueFromQMetaObject<QWidget>(&eng);
 #endif
-    QCOMPARE(qclass.isValid(), true);
+    QVERIFY(!qclass.isUndefined());
     QCOMPARE(qclass.isQMetaObject(), true);
     QCOMPARE(qclass.toQMetaObject(), &QObject::staticMetaObject);
     QCOMPARE(qclass.isCallable(), true);
     QVERIFY(qclass.property("prototype").isObject());
 
-    QCOMPARE(qclass2.isValid(), true);
+    QVERIFY(!qclass2.isUndefined());
     QCOMPARE(qclass2.isQMetaObject(), true);
     QCOMPARE(qclass2.toQMetaObject(), &QWidget::staticMetaObject);
     QCOMPARE(qclass2.isCallable(), true);
@@ -1288,7 +1286,7 @@ void tst_QJSEngine::newActivationObject()
     QScriptEngine eng;
     QScriptValue act = eng.newActivationObject();
     QEXPECT_FAIL("", "", Continue);
-    QCOMPARE(act.isValid(), true);
+    QVERIFY(!act.isUndefined());
     QEXPECT_FAIL("", "", Continue);
     QCOMPARE(act.isObject(), true);
     QVERIFY(!act.isCallable());
@@ -1296,7 +1294,7 @@ void tst_QJSEngine::newActivationObject()
     act.setProperty("prop", v);
     QEXPECT_FAIL("", "", Continue);
     QCOMPARE(act.property("prop").strictlyEquals(v), true);
-    QCOMPARE(act.scope().isValid(), false);
+    QVERIFY(act.scope().isUndefined());
     QEXPECT_FAIL("", "", Continue);
     QVERIFY(act.prototype().isNull());
 }
@@ -1311,9 +1309,9 @@ void tst_QJSEngine::getSetGlobalObjectSimple()
     engine.evaluate("var bar = 100");
     engine.setGlobalObject(object);
     engine.evaluate("rab = 100");
-    QVERIFY(engine.globalObject().property("rab").isValid());
-    QVERIFY(engine.globalObject().property("foo").isValid());
-    QVERIFY(!engine.globalObject().property("bar").isValid());
+    QVERIFY(!engine.globalObject().property("rab").isUndefined());
+    QVERIFY(!engine.globalObject().property("foo").isUndefined());
+    QVERIFY(engine.globalObject().property("bar").isUndefined());
 }
 
 void tst_QJSEngine::getSetGlobalObject()
@@ -1324,7 +1322,7 @@ void tst_QJSEngine::getSetGlobalObject()
     collectGarbage_helper(eng);
 
     glob = eng.globalObject();
-    QCOMPARE(glob.isValid(), true);
+    QVERIFY(!glob.isUndefined());
     QCOMPARE(glob.isObject(), true);
     QVERIFY(!glob.isCallable());
     QVERIFY(eng.currentContext()->thisObject().strictlyEquals(glob));
@@ -1332,7 +1330,7 @@ void tst_QJSEngine::getSetGlobalObject()
     QEXPECT_FAIL("", "FIXME: Do we really want to enforce this? ECMA standard says that it is implementation dependent, skipping for now", Continue);
     QCOMPARE(glob.toString(), QString::fromLatin1("[object global]"));
     // prototype should be Object.prototype
-    QCOMPARE(glob.prototype().isValid(), true);
+    QVERIFY(!glob.prototype().isUndefined());
     QCOMPARE(glob.prototype().isObject(), true);
     QEXPECT_FAIL("", "FIXME: Do we really want to enforce this? ECMA standard says that it is implementation dependent, skipping for now", Continue);
     QCOMPARE(glob.prototype().strictlyEquals(eng.evaluate("Object.prototype")), true);
@@ -1365,7 +1363,7 @@ void tst_QJSEngine::getSetGlobalObject()
     QVERIFY(eng.currentContext()->thisObject().strictlyEquals(obj));
     QVERIFY(eng.currentContext()->activationObject().strictlyEquals(obj));
 
-    QVERIFY(!obj.property("foo").isValid());
+    QVERIFY(obj.property("foo").isUndefined());
     eng.evaluate("var foo = 123");
     {
         QScriptValue ret = obj.property("foo");
@@ -1373,7 +1371,7 @@ void tst_QJSEngine::getSetGlobalObject()
         QCOMPARE(ret.toInt(), 123);
     }
 
-    QVERIFY(!obj.property("bar").isValid());
+    QVERIFY(obj.property("bar").isUndefined());
     eng.evaluate("bar = 456");
     {
         QScriptValue ret = obj.property("bar");
@@ -1381,7 +1379,7 @@ void tst_QJSEngine::getSetGlobalObject()
         QCOMPARE(ret.toInt(), 456);
     }
 
-    QVERIFY(!obj.property("baz").isValid());
+    QVERIFY(obj.property("baz").isUndefined());
     eng.evaluate("this['baz'] = 789");
     {
         QScriptValue ret = obj.property("baz");
@@ -1399,7 +1397,7 @@ void tst_QJSEngine::getSetGlobalObject()
         QScriptValue ret = eng.evaluate("delete foo");
         QVERIFY(ret.isBool());
         QVERIFY(ret.toBool());
-        QVERIFY(!obj.property("foo").isValid());
+        QVERIFY(obj.property("foo").isUndefined());
     }
 
     // Getter/setter property.
@@ -1588,19 +1586,19 @@ void tst_QJSEngine::createGlobalObjectProperty()
     // create property with no attributes
     {
         QString name = QString::fromLatin1("foo");
-        QVERIFY(!global.property(name).isValid());
+        QVERIFY(global.property(name).isUndefined());
         QJSValue val(123);
         global.setProperty(name, val);
         QVERIFY(global.property(name).equals(val));
         QVERIFY(global.propertyFlags(name) == 0);
-        global.setProperty(name, QJSValue());
-        QVERIFY(!global.property(name).isValid());
+        global.deleteProperty(name);
+        QVERIFY(global.property(name).isUndefined());
     }
     // create property with attributes
 #if 0 // ###FIXME: setProperty with flags is not supported
     {
         QString name = QString::fromLatin1("bar");
-        QVERIFY(!global.property(name).isValid());
+        QVERIFY(global.property(name).isUndefined());
         QScriptValue val(QString::fromLatin1("ciao"));
         QScriptValue::PropertyFlags flags = QScriptValue::ReadOnly | QScriptValue::SkipInEnumeration;
         global.setProperty(name, val, flags);
@@ -1608,7 +1606,7 @@ void tst_QJSEngine::createGlobalObjectProperty()
         //QEXPECT_FAIL("", "QTBUG-6134: custom Global Object properties don't retain attributes", Continue);
         QCOMPARE(global.propertyFlags(name), flags);
         global.setProperty(name, QScriptValue());
-        QVERIFY(!global.property(name).isValid());
+        QVERIFY(global.property(name).isUndefined());
     }
 #endif
 }
@@ -1718,7 +1716,7 @@ void tst_QJSEngine::customGlobalObjectWithPrototype()
             QVERIFY(ret.isCallable());
             QVERIFY(ret.strictlyEquals(global.property("print")));
         }
-        QVERIFY(!anotherProto.property("print").isValid());
+        QVERIFY(anotherProto.property("print").isUndefined());
     }
 }
 #endif
@@ -2218,7 +2216,7 @@ void tst_QJSEngine::uncaughtException()
             eng.clearExceptions();
             QVERIFY(!eng.hasUncaughtException());
             QCOMPARE(eng.uncaughtExceptionLineNumber(), -1);
-            QVERIFY(!eng.uncaughtException().isValid());
+            QVERIFY(eng.uncaughtException().isUndefined());
 
             eng.evaluate("2 = 3");
             QVERIFY(eng.hasUncaughtException());
@@ -2235,7 +2233,7 @@ void tst_QJSEngine::uncaughtException()
         {
             QScriptValue ret = eng.evaluate("a = 10");
             QVERIFY(!eng.hasUncaughtException());
-            QVERIFY(!eng.uncaughtException().isValid());
+            QVERIFY(eng.uncaughtException().isUndefined());
         }
         {
             QScriptValue ret = eng.evaluate("1 = 2");
@@ -2279,7 +2277,7 @@ void tst_QJSEngine::getSetDefaultPrototype_int()
     QScriptEngine eng;
 
     QScriptValue object = eng.newObject();
-    QCOMPARE(eng.defaultPrototype(qMetaTypeId<int>()).isValid(), false);
+    QVERIFY(eng.defaultPrototype(qMetaTypeId<int>()).isUndefined());
     eng.setDefaultPrototype(qMetaTypeId<int>(), object);
     QCOMPARE(eng.defaultPrototype(qMetaTypeId<int>()).strictlyEquals(object), true);
     QScriptValue value = eng.newVariant(int(123));
@@ -2287,7 +2285,7 @@ void tst_QJSEngine::getSetDefaultPrototype_int()
     QCOMPARE(value.prototype().strictlyEquals(object), true);
 
     eng.setDefaultPrototype(qMetaTypeId<int>(), QScriptValue());
-    QCOMPARE(eng.defaultPrototype(qMetaTypeId<int>()).isValid(), false);
+    QVERIFY(eng.defaultPrototype(qMetaTypeId<int>()).isUndefined());
     QScriptValue value2 = eng.newVariant(int(123));
     QCOMPARE(value2.prototype().strictlyEquals(object), false);
 }
@@ -2297,7 +2295,7 @@ void tst_QJSEngine::getSetDefaultPrototype_customType()
     QScriptEngine eng;
 
     QScriptValue object = eng.newObject();
-    QCOMPARE(eng.defaultPrototype(qMetaTypeId<Foo>()).isValid(), false);
+    QVERIFY(eng.defaultPrototype(qMetaTypeId<Foo>()).isUndefined());
     eng.setDefaultPrototype(qMetaTypeId<Foo>(), object);
     QCOMPARE(eng.defaultPrototype(qMetaTypeId<Foo>()).strictlyEquals(object), true);
     QScriptValue value = eng.newVariant(qVariantFromValue(Foo()));
@@ -2305,7 +2303,7 @@ void tst_QJSEngine::getSetDefaultPrototype_customType()
     QCOMPARE(value.prototype().strictlyEquals(object), true);
 
     eng.setDefaultPrototype(qMetaTypeId<Foo>(), QScriptValue());
-    QCOMPARE(eng.defaultPrototype(qMetaTypeId<Foo>()).isValid(), false);
+    QVERIFY(eng.defaultPrototype(qMetaTypeId<Foo>()).isUndefined());
     QScriptValue value2 = eng.newVariant(qVariantFromValue(Foo()));
     QCOMPARE(value2.prototype().strictlyEquals(object), false);
 }
@@ -2558,8 +2556,6 @@ void tst_QJSEngine::valueConversion_QVariant()
 
         QJSValue val1 = eng.toScriptValue(tmp1);
         QJSValue val2 = eng.toScriptValue(tmp2);
-        QVERIFY(val1.isValid());
-        QVERIFY(val2.isValid());
         QVERIFY(val1.isUndefined());
         QEXPECT_FAIL("", "Variant are unrwapped, maybe we should not...", Continue);
         QVERIFY(!val2.isUndefined());
@@ -2577,8 +2573,8 @@ void tst_QJSEngine::valueConversion_QVariant()
 
         QJSValue val1 = eng.toScriptValue(tmp2);
         QJSValue val2 = eng.toScriptValue(tmp3);
-        QVERIFY(val1.isValid());
-        QVERIFY(val2.isValid());
+        QVERIFY(!val1.isUndefined());
+        QVERIFY(!val2.isUndefined());
         QEXPECT_FAIL("", "Variant are unrwapped, maybe we should not...", Continue);
         QVERIFY(val1.isVariant());
         QEXPECT_FAIL("", "Variant are unrwapped, maybe we should not...", Continue);
@@ -2742,8 +2738,8 @@ void tst_QJSEngine::valueConversion_regExp()
 #if 0 // FIXME: No qScriptValueFromValue
 void tst_QJSEngine::qScriptValueFromValue_noEngine()
 {
-    QVERIFY(!qScriptValueFromValue(0, 123).isValid());
-    QVERIFY(!qScriptValueFromValue(0, QVariant(123)).isValid());
+    QVERIFY(qScriptValueFromValue(0, 123).isUndefined());
+    QVERIFY(qScriptValueFromValue(0, QVariant(123)).isUndefined());
 }
 #endif
 
@@ -2783,10 +2779,10 @@ void tst_QJSEngine::importExtension()
     {
         QScriptEngine eng;
         for (int x = 0; x < 2; ++x) {
-            QCOMPARE(eng.globalObject().property("com").isValid(), x == 1);
+            QCOMPARE(!eng.globalObject().property("com").isUndefined(), x == 1);
             QScriptValue ret = eng.importExtension("com.trolltech");
             QCOMPARE(eng.hasUncaughtException(), false);
-            QCOMPARE(ret.isUndefined(), true);
+            QVERIFY(ret.isUndefined());
 
             QScriptValue com = eng.globalObject().property("com");
             QCOMPARE(com.isObject(), true);
@@ -3717,7 +3713,7 @@ void tst_QJSEngine::abortEvaluation()
         switch (receiver.resultType) {
         case EventReceiver3::None:
             QVERIFY(!eng.hasUncaughtException());
-            QVERIFY(!ret.isValid());
+            QVERIFY(ret.isUndefined());
             break;
         case EventReceiver3::Number:
             QVERIFY(!eng.hasUncaughtException());
@@ -3760,7 +3756,7 @@ void tst_QJSEngine::abortEvaluation_tryCatch()
         switch (receiver.resultType) {
         case EventReceiver3::None:
             QVERIFY(!eng.hasUncaughtException());
-            QVERIFY(!ret.isValid());
+            QVERIFY(ret.isUndefined());
             break;
         case EventReceiver3::Number:
             QVERIFY(!eng.hasUncaughtException());
@@ -3786,7 +3782,7 @@ void tst_QJSEngine::abortEvaluation_fromNative()
     QScriptValue fun = eng.newFunction(myFunctionAbortingEvaluation);
     eng.globalObject().setProperty("myFunctionAbortingEvaluation", fun);
     QScriptValue ret = eng.evaluate("myFunctionAbortingEvaluation()");
-    QVERIFY(!ret.isValid());
+    QVERIFY(ret.isUndefined());
 }
 
 class ThreadedEngine : public QThread {
@@ -3993,7 +3989,7 @@ void tst_QJSEngine::argumentsProperty_globalContext()
         QCOMPARE(ret.toInt(), 10);
     }
     QVERIFY(eng.evaluate("delete arguments").toBool());
-    QVERIFY(!eng.globalObject().property("arguments").isValid());
+    QVERIFY(eng.globalObject().property("arguments").isUndefined());
 }
 
 void tst_QJSEngine::argumentsProperty_JS()
@@ -4007,13 +4003,13 @@ void tst_QJSEngine::argumentsProperty_JS()
     }
     {
         QJSEngine eng;
-        QVERIFY(!eng.globalObject().property("arguments").isValid());
+        QVERIFY(eng.globalObject().property("arguments").isUndefined());
         // This is testing ECMA-262 compliance. In function calls, "arguments"
         // appears like a local variable, and it can be replaced.
         QJSValue ret = eng.evaluate("(function() { arguments = 456; return arguments; })()");
         QVERIFY(ret.isNumber());
         QCOMPARE(ret.toInt(), 456);
-        QVERIFY(!eng.globalObject().property("arguments").isValid());
+        QVERIFY(eng.globalObject().property("arguments").isUndefined());
     }
 }
 
@@ -4297,7 +4293,7 @@ void tst_QJSEngine::jsFunctionDeclarationAsStatement()
     // check this behavior.
 
     QJSEngine eng;
-    QVERIFY(!eng.globalObject().property("bar").isValid());
+    QVERIFY(eng.globalObject().property("bar").isUndefined());
     eng.evaluate("function foo(arg) {\n"
                  "  if (arg == 'bar')\n"
                  "    function bar() { return 'bar'; }\n"
@@ -4305,24 +4301,24 @@ void tst_QJSEngine::jsFunctionDeclarationAsStatement()
                  "    function baz() { return 'baz'; }\n"
                  "  return (arg == 'bar') ? bar : baz;\n"
                  "}");
-    QVERIFY(!eng.globalObject().property("bar").isValid());
-    QVERIFY(!eng.globalObject().property("baz").isValid());
+    QVERIFY(eng.globalObject().property("bar").isUndefined());
+    QVERIFY(eng.globalObject().property("baz").isUndefined());
     QVERIFY(eng.evaluate("foo").isCallable());
     {
         QJSValue ret = eng.evaluate("foo('bar')");
         QVERIFY(ret.isCallable());
         QJSValue ret2 = ret.call();
         QCOMPARE(ret2.toString(), QString::fromLatin1("bar"));
-        QVERIFY(!eng.globalObject().property("bar").isValid());
-        QVERIFY(!eng.globalObject().property("baz").isValid());
+        QVERIFY(eng.globalObject().property("bar").isUndefined());
+        QVERIFY(eng.globalObject().property("baz").isUndefined());
     }
     {
         QJSValue ret = eng.evaluate("foo('baz')");
         QVERIFY(ret.isCallable());
         QJSValue ret2 = ret.call();
         QCOMPARE(ret2.toString(), QString::fromLatin1("baz"));
-        QVERIFY(!eng.globalObject().property("bar").isValid());
-        QVERIFY(!eng.globalObject().property("baz").isValid());
+        QVERIFY(eng.globalObject().property("bar").isUndefined());
+        QVERIFY(eng.globalObject().property("baz").isUndefined());
     }
 }
 
@@ -4343,13 +4339,14 @@ void tst_QJSEngine::stringObjects()
             QCOMPARE(obj.property(pname).toString(), QString(str.at(i)));
             QEXPECT_FAIL("", "FIXME: This is V8 issue 862. ECMA script standard 15.5.5.2 compliance.", Continue);
             QCOMPARE(obj.propertyFlags(pname), QJSValue::PropertyFlags(QJSValue::Undeletable | QJSValue::ReadOnly));
-            obj.setProperty(pname, QJSValue());
+            QEXPECT_FAIL("", "FIXME: This is V8 issue 862. ECMA script standard 15.5.5.2 compliance.", Continue);
+            QVERIFY(!obj.deleteProperty(pname));
             obj.setProperty(pname, QJSValue(&eng, 123));
             QVERIFY(obj.property(pname).isString());
             QCOMPARE(obj.property(pname).toString(), QString(str.at(i)));
         }
-        QVERIFY(!obj.property("-1").isValid());
-        QVERIFY(!obj.property(QString::number(str.length())).isValid());
+        QVERIFY(obj.property("-1").isUndefined());
+        QVERIFY(obj.property(QString::number(str.length())).isUndefined());
 
         QJSValue val(&eng, 123);
         obj.setProperty("-1", val);
@@ -4950,14 +4947,14 @@ void tst_QJSEngine::reentrancy_typeConversion()
         QCOMPARE(foo2.x, 12);
         QCOMPARE(foo2.y, 34);
     }
-    QVERIFY(!eng1.defaultPrototype(qMetaTypeId<Foo>()).isValid());
-    QVERIFY(!eng2.defaultPrototype(qMetaTypeId<Foo>()).isValid());
+    QVERIFY(eng1.defaultPrototype(qMetaTypeId<Foo>()).isUndefined());
+    QVERIFY(eng2.defaultPrototype(qMetaTypeId<Foo>()).isUndefined());
     QScriptValue proto1 = eng1.newObject();
     eng1.setDefaultPrototype(qMetaTypeId<Foo>(), proto1);
-    QVERIFY(!eng2.defaultPrototype(qMetaTypeId<Foo>()).isValid());
+    QVERIFY(eng2.defaultPrototype(qMetaTypeId<Foo>()).isUndefined());
     QScriptValue proto2 = eng2.newObject();
     eng2.setDefaultPrototype(qMetaTypeId<Foo>(), proto2);
-    QVERIFY(eng2.defaultPrototype(qMetaTypeId<Foo>()).isValid());
+    QVERIFY(!eng2.defaultPrototype(qMetaTypeId<Foo>()).isUndefined());
     QVERIFY(eng1.defaultPrototype(qMetaTypeId<Foo>()).strictlyEquals(proto1));
 }
 #endif
@@ -4966,10 +4963,10 @@ void tst_QJSEngine::reentrancy_globalObjectProperties()
 {
     QJSEngine eng1;
     QJSEngine eng2;
-    QVERIFY(!eng2.globalObject().property("a").isValid());
+    QVERIFY(eng2.globalObject().property("a").isUndefined());
     eng1.evaluate("a = 10");
     QVERIFY(eng1.globalObject().property("a").isNumber());
-    QVERIFY(!eng2.globalObject().property("a").isValid());
+    QVERIFY(eng2.globalObject().property("a").isUndefined());
     eng2.evaluate("a = 20");
     QVERIFY(eng2.globalObject().property("a").isNumber());
     QCOMPARE(eng1.globalObject().property("a").toInt(), 10);
@@ -5095,13 +5092,13 @@ void tst_QJSEngine::installTranslatorFunctions()
 {
     QScriptEngine eng;
     QScriptValue global = eng.globalObject();
-    QVERIFY(!global.property("qsTranslate").isValid());
-    QVERIFY(!global.property("QT_TRANSLATE_NOOP").isValid());
-    QVERIFY(!global.property("qsTr").isValid());
-    QVERIFY(!global.property("QT_TR_NOOP").isValid());
-    QVERIFY(!global.property("qsTrId").isValid());
-    QVERIFY(!global.property("QT_TRID_NOOP").isValid());
-    QVERIFY(!global.property("String").property("prototype").property("arg").isValid());
+    QVERIFY(global.property("qsTranslate").isUndefined());
+    QVERIFY(global.property("QT_TRANSLATE_NOOP").isUndefined());
+    QVERIFY(global.property("qsTr").isUndefined());
+    QVERIFY(global.property("QT_TR_NOOP").isUndefined());
+    QVERIFY(global.property("qsTrId").isUndefined());
+    QVERIFY(global.property("QT_TRID_NOOP").isUndefined());
+    QVERIFY(global.property("String").property("prototype").property("arg").isUndefined());
 
     eng.installTranslatorFunctions();
     QVERIFY(global.property("qsTranslate").isCallable());
@@ -5582,13 +5579,13 @@ void tst_QJSEngine::functionScopes()
         QEXPECT_FAIL("", "QScriptValue::scope() is internal, not implemented", Abort);
         QVERIFY(fun.scope().isObject());
         QVERIFY(fun.scope().strictlyEquals(eng.globalObject()));
-        QVERIFY(!eng.globalObject().scope().isValid());
+        QVERIFY(eng.globalObject().scope().isUndefined());
     }
     {
         QScriptValue fun = eng.globalObject().property("Object");
         QVERIFY(fun.isCallable());
         // native built-in functions don't have scope
-        QVERIFY(!fun.scope().isValid());
+        QVERIFY(fun.scope().isUndefined());
     }
     {
         // closure
@@ -5873,7 +5870,7 @@ void tst_QJSEngine::evaluateProgram_empty()
         QScriptProgram program;
         QVERIFY(program.isNull());
         QScriptValue ret = eng.evaluate(program);
-        QVERIFY(!ret.isValid());
+        QVERIFY(ret.isUndefined());
     }
 }
 #endif
@@ -5976,7 +5973,6 @@ void tst_QJSEngine::qRegExpInport()
     QJSValue rexp;
     rexp = eng.toScriptValue(rx);
 
-    QCOMPARE(rexp.isValid(), true);
     QCOMPARE(rexp.isRegExp(), true);
     QVERIFY(rexp.isCallable());
 
@@ -6110,7 +6106,7 @@ void tst_QJSEngine::newFixedStaticScopeObject()
     }
 
     // Property that doesn't exist.
-    QVERIFY(!scope.property("noSuchProperty").isValid());
+    QVERIFY(scope.property("noSuchProperty").isUndefined());
     QCOMPARE(scope.propertyFlags("noSuchProperty"), QScriptValue::PropertyFlags());
 
     // Write to writable property.
@@ -6193,9 +6189,9 @@ void tst_QJSEngine::newFixedStaticScopeObject()
 
     // As with normal JS, assigning to an undefined variable will create
     // the property on the Global Object, not the inner scope.
-    QVERIFY(!eng.globalObject().property("newProperty").isValid());
+    QVERIFY(eng.globalObject().property("newProperty").isUndefined());
     QVERIFY(eng.evaluate("(function() { newProperty = 789; })()").isUndefined());
-    QVERIFY(!scope.property("newProperty").isValid());
+    QVERIFY(!scope.property("newProperty").isUndefined());
     QVERIFY(eng.globalObject().property("newProperty").isNumber());
 
     // Nested static scope.
@@ -6238,7 +6234,7 @@ void tst_QJSEngine::newGrowingStaticScopeObject()
 
     // Initially empty.
     QVERIFY(!QScriptValueIterator(scope).hasNext());
-    QVERIFY(!scope.property("foo").isValid());
+    QVERIFY(scope.property("foo").isUndefined());
 
     // Add a static property.
     scope.setProperty("foo", 123);
@@ -6345,7 +6341,7 @@ void tst_QJSEngine::scriptValueFromQMetaObject()
         QCOMPARE(meta.toQMetaObject(), &QScriptEngine::staticMetaObject);
         // Because of missing Q_SCRIPT_DECLARE_QMETAOBJECT() for QScriptEngine.
         QEXPECT_FAIL("", "FIXME: because construct never returns invalid values", Continue);
-        QVERIFY(!meta.callAsConstructor().isValid());
+        QVERIFY(meta.callAsConstructor().isUndefined());
     }
     {
         QScriptValue meta = eng.scriptValueFromQMetaObject<QStandardItemModel>();
diff --git a/tests/auto/declarative/qjsvalue/tst_qjsvalue.cpp b/tests/auto/declarative/qjsvalue/tst_qjsvalue.cpp
index d034b76c03..e478dc3fd3 100644
--- a/tests/auto/declarative/qjsvalue/tst_qjsvalue.cpp
+++ b/tests/auto/declarative/qjsvalue/tst_qjsvalue.cpp
@@ -62,7 +62,7 @@ void tst_QJSValue::ctor_invalid()
     QJSEngine eng;
     {
         QJSValue v;
-        QCOMPARE(v.isValid(), false);
+        QVERIFY(v.isUndefined());
         QCOMPARE(v.engine(), (QJSEngine *)0);
     }
 }
@@ -72,8 +72,7 @@ void tst_QJSValue::ctor_undefinedWithEngine()
     QJSEngine eng;
     {
         QJSValue v(&eng, QJSValue::UndefinedValue);
-        QCOMPARE(v.isValid(), true);
-        QCOMPARE(v.isUndefined(), true);
+        QVERIFY(v.isUndefined());
         QCOMPARE(v.isObject(), false);
         QCOMPARE(v.engine(), &eng);
     }
@@ -84,7 +83,7 @@ void tst_QJSValue::ctor_nullWithEngine()
     QJSEngine eng;
     {
         QJSValue v(&eng, QJSValue::NullValue);
-        QCOMPARE(v.isValid(), true);
+        QVERIFY(!v.isUndefined());
         QCOMPARE(v.isNull(), true);
         QCOMPARE(v.isObject(), false);
         QCOMPARE(v.engine(), &eng);
@@ -96,7 +95,7 @@ void tst_QJSValue::ctor_boolWithEngine()
     QJSEngine eng;
     {
         QJSValue v(&eng, false);
-        QCOMPARE(v.isValid(), true);
+        QVERIFY(!v.isUndefined());
         QCOMPARE(v.isBool(), true);
         QCOMPARE(v.isBool(), true);
         QCOMPARE(v.isObject(), false);
@@ -110,7 +109,7 @@ void tst_QJSValue::ctor_intWithEngine()
     QJSEngine eng;
     {
         QJSValue v(&eng, int(1));
-        QCOMPARE(v.isValid(), true);
+        QVERIFY(!v.isUndefined());
         QCOMPARE(v.isNumber(), true);
         QCOMPARE(v.isObject(), false);
         QCOMPARE(v.toNumber(), 1.0);
@@ -127,7 +126,7 @@ void tst_QJSValue::ctor_int()
     }
     {
         QJSValue v(int(1));
-        QCOMPARE(v.isValid(), true);
+        QVERIFY(!v.isUndefined());
         QCOMPARE(v.isNumber(), true);
         QCOMPARE(v.isObject(), false);
         QCOMPARE(v.toNumber(), 1.0);
@@ -140,7 +139,7 @@ void tst_QJSValue::ctor_uintWithEngine()
     QJSEngine eng;
     {
         QJSValue v(&eng, uint(1));
-        QCOMPARE(v.isValid(), true);
+        QVERIFY(!v.isUndefined());
         QCOMPARE(v.isNumber(), true);
         QCOMPARE(v.isObject(), false);
         QCOMPARE(v.toNumber(), 1.0);
@@ -157,7 +156,7 @@ void tst_QJSValue::ctor_uint()
     }
     {
         QJSValue v(uint(1));
-        QCOMPARE(v.isValid(), true);
+        QVERIFY(!v.isUndefined());
         QCOMPARE(v.isNumber(), true);
         QCOMPARE(v.isObject(), false);
         QCOMPARE(v.toNumber(), 1.0);
@@ -170,7 +169,7 @@ void tst_QJSValue::ctor_floatWithEngine()
     QJSEngine eng;
     {
         QJSValue v(&eng, 1.0);
-        QCOMPARE(v.isValid(), true);
+        QVERIFY(!v.isUndefined());
         QCOMPARE(v.isNumber(), true);
         QCOMPARE(v.isObject(), false);
         QCOMPARE(v.toNumber(), 1.0);
@@ -187,7 +186,7 @@ void tst_QJSValue::ctor_float()
     }
     {
         QJSValue v(1.0);
-        QCOMPARE(v.isValid(), true);
+        QVERIFY(!v.isUndefined());
         QCOMPARE(v.isNumber(), true);
         QCOMPARE(v.isObject(), false);
         QCOMPARE(v.toNumber(), 1.0);
@@ -200,7 +199,7 @@ void tst_QJSValue::ctor_stringWithEngine()
     QJSEngine eng;
     {
         QJSValue v(&eng, QLatin1String("ciao"));
-        QCOMPARE(v.isValid(), true);
+        QVERIFY(!v.isUndefined());
         QCOMPARE(v.isString(), true);
         QCOMPARE(v.isObject(), false);
         QCOMPARE(v.toString(), QLatin1String("ciao"));
@@ -212,7 +211,7 @@ void tst_QJSValue::ctor_string()
 {
     {
         QJSValue v(QString("ciao"));
-        QCOMPARE(v.isValid(), true);
+        QVERIFY(!v.isUndefined());
         QCOMPARE(v.isString(), true);
         QCOMPARE(v.isObject(), false);
         QCOMPARE(v.toString(), QLatin1String("ciao"));
@@ -220,7 +219,7 @@ void tst_QJSValue::ctor_string()
     }
     {
         QJSValue v("ciao");
-        QCOMPARE(v.isValid(), true);
+        QVERIFY(!v.isUndefined());
         QCOMPARE(v.isString(), true);
         QCOMPARE(v.isObject(), false);
         QCOMPARE(v.toString(), QLatin1String("ciao"));
@@ -264,8 +263,7 @@ void tst_QJSValue::ctor_copyAndAssignWithEngine()
 void tst_QJSValue::ctor_undefined()
 {
     QJSValue v(QJSValue::UndefinedValue);
-    QCOMPARE(v.isValid(), true);
-    QCOMPARE(v.isUndefined(), true);
+    QVERIFY(v.isUndefined());
     QCOMPARE(v.isObject(), false);
     QCOMPARE(v.engine(), (QJSEngine *)0);
 }
@@ -273,7 +271,7 @@ void tst_QJSValue::ctor_undefined()
 void tst_QJSValue::ctor_null()
 {
     QJSValue v(QJSValue::NullValue);
-    QCOMPARE(v.isValid(), true);
+    QVERIFY(!v.isUndefined());
     QCOMPARE(v.isNull(), true);
     QCOMPARE(v.isObject(), false);
     QCOMPARE(v.engine(), (QJSEngine *)0);
@@ -282,7 +280,7 @@ void tst_QJSValue::ctor_null()
 void tst_QJSValue::ctor_bool()
 {
     QJSValue v(false);
-    QCOMPARE(v.isValid(), true);
+    QVERIFY(!v.isUndefined());
     QCOMPARE(v.isBool(), true);
     QCOMPARE(v.isBool(), true);
     QCOMPARE(v.isObject(), false);
@@ -416,7 +414,7 @@ void tst_QJSValue::toString()
     }
 
     QJSValue inv = QJSValue();
-    QCOMPARE(inv.toString(), QString());
+    QCOMPARE(inv.toString(), QString::fromLatin1("undefined"));
 
     // V2 constructors
     {
@@ -496,8 +494,8 @@ void tst_QJSValue::toNumber()
 #endif
 
     QJSValue inv = QJSValue();
-    QCOMPARE(inv.toNumber(), 0.0);
-    QCOMPARE(qjsvalue_cast<qreal>(inv), 0.0);
+    QVERIFY(qIsNaN(inv.toNumber()));
+    QVERIFY(qIsNaN(qjsvalue_cast<qreal>(inv)));
 
     // V2 constructors
     {
@@ -1495,7 +1493,6 @@ void tst_QJSValue::getSetProperty_HooliganTask183072()
 
 void tst_QJSValue::getSetProperty_propertyRemoval()
 {
-    // test property removal (setProperty(QJSValue()))
     QJSEngine eng;
     QJSValue object = eng.newObject();
     QJSValue str = QJSValue(&eng, QLatin1String("bar"));
@@ -1505,17 +1502,17 @@ void tst_QJSValue::getSetProperty_propertyRemoval()
     QCOMPARE(object.property("foo").strictlyEquals(num), true);
     object.setProperty("bar", str);
     QCOMPARE(object.property("bar").strictlyEquals(str), true);
-    object.setProperty("foo", QJSValue());
-    QCOMPARE(object.property("foo").isValid(), false);
+    QVERIFY(object.deleteProperty("foo"));
+    QVERIFY(!object.hasOwnProperty("foo"));
     QCOMPARE(object.property("bar").strictlyEquals(str), true);
     object.setProperty("foo", num);
     QCOMPARE(object.property("foo").strictlyEquals(num), true);
     QCOMPARE(object.property("bar").strictlyEquals(str), true);
-    object.setProperty("bar", QJSValue());
-    QCOMPARE(object.property("bar").isValid(), false);
+    QVERIFY(object.deleteProperty("bar"));
+    QVERIFY(!object.hasOwnProperty("bar"));
     QCOMPARE(object.property("foo").strictlyEquals(num), true);
-    object.setProperty("foo", QJSValue());
-    object.setProperty("foo", QJSValue());
+    QVERIFY(object.deleteProperty("foo"));
+    QVERIFY(!object.hasOwnProperty("foo"));
 
     eng.globalObject().setProperty("object3", object);
     QCOMPARE(eng.evaluate("object3.hasOwnProperty('foo')")
@@ -1523,7 +1520,7 @@ void tst_QJSValue::getSetProperty_propertyRemoval()
     object.setProperty("foo", num);
     QCOMPARE(eng.evaluate("object3.hasOwnProperty('foo')")
              .strictlyEquals(QJSValue(&eng, true)), true);
-    eng.globalObject().setProperty("object3", QJSValue());
+    QVERIFY(eng.globalObject().deleteProperty("object3"));
     QCOMPARE(eng.evaluate("this.hasOwnProperty('object3')")
              .strictlyEquals(QJSValue(&eng, false)), true);
 }
@@ -1561,7 +1558,8 @@ void tst_QJSValue::getSetProperty_twoEngines()
     QJSValue otherNum = QJSValue(&otherEngine, 123);
     QTest::ignoreMessage(QtWarningMsg, "QJSValue::setProperty(oof) failed: cannot set value created in a different engine");
     object.setProperty("oof", otherNum);
-    QCOMPARE(object.property("oof").isValid(), false);
+    QVERIFY(!object.hasOwnProperty("oof"));
+    QVERIFY(object.property("oof").isUndefined());
 }
 
 
@@ -1573,7 +1571,7 @@ void tst_QJSValue::getSetProperty_gettersAndSetters()
     QJSValue num = QJSValue(&eng, 123.0);
     QJSValue object = eng.newObject();
     for (int x = 0; x < 2; ++x) {
-        object.setProperty("foo", QJSValue());
+        object.deleteProperty("foo");
         // getter() returns this.x
         object.setProperty("foo", eng.newFunction(getter),
                             QJSValue::PropertyGetter | QJSValue::UserRange);
@@ -1618,7 +1616,7 @@ void tst_QJSValue::getSetProperty_gettersAndSetters()
     }
 
     for (int x = 0; x < 2; ++x) {
-        object.setProperty("foo", QJSValue());
+        object.deleteProperty("foo");
         // setter() sets this.x
         object.setProperty("foo", eng.newFunction(setter), QJSValue::PropertySetter);
         object.setProperty("foo", str);
@@ -1646,7 +1644,7 @@ void tst_QJSValue::getSetProperty_gettersAndSetters()
     }
 
     // use a single function as both getter and setter
-    object.setProperty("foo", QJSValue());
+    object.deleteProperty("foo");
     object.setProperty("foo", eng.newFunction(getterSetter),
                         QJSValue::PropertyGetter | QJSValue::PropertySetter);
     QCOMPARE(object.propertyFlags("foo"),
@@ -1800,7 +1798,7 @@ void tst_QJSValue::getSetProperty_array()
     QCOMPARE(array.property("length").toUInt(), quint32(2));
     array.setProperty("length", QJSValue(&eng, 1));
     QCOMPARE(array.property("length").toUInt(), quint32(1));
-    QCOMPARE(array.property(1).isValid(), false);
+    QVERIFY(array.property(1).isUndefined());
 }
 
 void tst_QJSValue::getSetProperty_gettersAndSettersStupid()
@@ -1863,7 +1861,7 @@ void tst_QJSValue::getSetProperty()
 
     QJSValue inv;
     inv.setProperty("foo", num);
-    QCOMPARE(inv.property("foo").isValid(), false);
+    QCOMPARE(inv.property("foo").isUndefined(), true);
 
     eng.globalObject().setProperty("object", object);
 
@@ -1916,7 +1914,7 @@ void tst_QJSValue::getSetProperty()
         QCOMPARE(ret.strictlyEquals(QJSValue(&eng, true)), true);
     }
     // should still be deletable from C++
-    object.setProperty("undeletableProperty", QJSValue());
+    object.deleteProperty("undeletableProperty");
     QEXPECT_FAIL("", "QTBUG-17617: With JSC-based back-end, undeletable properties can't be deleted from C++", Continue);
     QVERIFY(!object.property("undeletableProperty").isValid());
     QEXPECT_FAIL("", "QTBUG-17617: With JSC-based back-end, undeletable properties can't be deleted from C++", Continue);
@@ -1981,7 +1979,7 @@ void tst_QJSValue::getSetProperty()
     // using interned strings
     QScriptString foo = eng.toStringHandle("foo");
 
-    object.setProperty(foo, QJSValue());
+    QVERIFY(object.deleteProperty(foo));
     QVERIFY(!object.property(foo).isValid());
 
     object.setProperty(foo, num);
@@ -2068,7 +2066,7 @@ void tst_QJSValue::getSetPrototype_invalidPrototype()
     QJSValue proto = object.prototype();
     QVERIFY(object.prototype().strictlyEquals(proto));
     inv.setPrototype(object);
-    QCOMPARE(inv.prototype().isValid(), false);
+    QVERIFY(inv.prototype().isUndefined());
     object.setPrototype(inv);
     QVERIFY(object.prototype().strictlyEquals(proto));
 }
@@ -2566,8 +2564,7 @@ void tst_QJSValue::call_invalidArguments()
             args << QJSValue();
             QJSValue ret = fun.callWithInstance(args);
             QVERIFY(!eng.hasUncaughtException());
-            QCOMPARE(ret.isValid(), true);
-            QCOMPARE(ret.isUndefined(), true);
+            QVERIFY(ret.isUndefined());
         }
     }
     {
@@ -2576,8 +2573,7 @@ void tst_QJSValue::call_invalidArguments()
             QJSValueList args;
             args << QJSValue();
             QJSValue ret = fun.call(args);
-            QCOMPARE(ret.isValid(), true);
-            QCOMPARE(ret.isUndefined(), true);
+            QVERIFY(ret.isUndefined());
         }
     }
     {
@@ -2586,7 +2582,7 @@ void tst_QJSValue::call_invalidArguments()
             QJSValueList args;
             args << QJSValue() << QJSValue();
             QJSValue ret = fun.call(args);
-            QCOMPARE(ret.isValid(), true);
+            QVERIFY(!ret.isUndefined());
             QCOMPARE(ret.isNumber(), true);
             QCOMPARE(qIsNaN(ret.toNumber()), true);
         }
@@ -2602,7 +2598,7 @@ void tst_QJSValue::call_invalidReturn()
     QJSValue fun = eng.newFunction(returnInvalidValue);
     eng.globalObject().setProperty("returnInvalidValue", fun);
     QJSValue ret = eng.evaluate("returnInvalidValue() + returnInvalidValue()");
-    QCOMPARE(ret.isValid(), true);
+    QVERIFY(!ret.isUndefined());
     QCOMPARE(ret.isNumber(), true);
     QCOMPARE(qIsNaN(ret.toNumber()), true);
 #endif
@@ -2619,11 +2615,11 @@ void tst_QJSValue::call_twoEngines()
     QTest::ignoreMessage(QtWarningMsg, "QJSValue::call() failed: "
                          "cannot call function with thisObject created in "
                          "a different engine");
-    QCOMPARE(fun.callWithInstance(object).isValid(), false);
+    QVERIFY(fun.callWithInstance(object).isUndefined());
     QTest::ignoreMessage(QtWarningMsg, "QJSValue::call() failed: "
                          "cannot call function with argument created in "
                          "a different engine");
-    QCOMPARE(fun.call(QJSValueList() << QJSValue(&eng, 123)).isValid(), false);
+    QVERIFY(fun.call(QJSValueList() << QJSValue(&eng, 123)).isUndefined());
     {
         QJSValue fun = eng.evaluate("Object");
         QVERIFY(fun.isCallable());
@@ -2703,7 +2699,7 @@ void tst_QJSValue::call_nonFunction()
 {
     // calling things that are not functions
     QFETCH(QJSValue, value);
-    QVERIFY(!value.call().isValid());
+    QVERIFY(value.call().isUndefined());
 }
 
 #if 0 // FIXME: no c-style callbacks
@@ -2743,7 +2739,7 @@ void tst_QJSValue::construct_nonFunction_data()
 void tst_QJSValue::construct_nonFunction()
 {
     QFETCH(QJSValue, value);
-    QVERIFY(!value.callAsConstructor().isValid());
+    QVERIFY(value.callAsConstructor().isUndefined());
 }
 
 void tst_QJSValue::construct_simple()
@@ -2752,6 +2748,7 @@ void tst_QJSValue::construct_simple()
     QJSValue fun = eng.evaluate("(function () { this.foo = 123; })");
     QVERIFY(fun.isCallable());
     QJSValue ret = fun.callAsConstructor();
+    QVERIFY(!ret.isUndefined());
     QVERIFY(ret.isObject());
     QVERIFY(ret.prototype().strictlyEquals(fun.property("prototype")));
     QCOMPARE(ret.property("foo").toInt(), 123);
@@ -2848,7 +2845,6 @@ void tst_QJSValue::construct()
     // construct with single array object as arguments
     QJSValue ret = fun.callAsConstructor(array);
     QVERIFY(!eng.hasUncaughtException());
-    QVERIFY(ret.isValid());
     QVERIFY(ret.isObject());
     QCOMPARE(ret.property(0).strictlyEquals(array.property(0)), true);
     QCOMPARE(ret.property(1).strictlyEquals(array.property(1)), true);
@@ -2885,9 +2881,9 @@ void tst_QJSValue::construct_twoEngines()
     QJSValue ctor = engine.evaluate("(function (a, b) { this.foo = 123; })");
     QJSValue arg(&otherEngine, 124567);
     QTest::ignoreMessage(QtWarningMsg, "QJSValue::callAsConstructor() failed: cannot construct function with argument created in a different engine");
-    QVERIFY(!ctor.callAsConstructor(QJSValueList() << arg).isValid());
+    QVERIFY(ctor.callAsConstructor(QJSValueList() << arg).isUndefined());
     QTest::ignoreMessage(QtWarningMsg, "QJSValue::callAsConstructor() failed: cannot construct function with argument created in a different engine");
-    QVERIFY(!ctor.callAsConstructor(QJSValueList() << arg << otherEngine.newObject()).isValid());
+    QVERIFY(ctor.callAsConstructor(QJSValueList() << arg << otherEngine.newObject()).isUndefined());
 }
 
 void tst_QJSValue::construct_constructorThrowsPrimitive()
@@ -3069,8 +3065,8 @@ void tst_QJSValue::equals()
     QCOMPARE(null.equals(null), true);
     QCOMPARE(undefined.equals(null), true);
     QCOMPARE(null.equals(undefined), true);
-    QCOMPARE(undefined.equals(QJSValue()), false);
-    QCOMPARE(null.equals(QJSValue()), false);
+    QVERIFY(undefined.equals(QJSValue()));
+    QVERIFY(null.equals(QJSValue()));
     QVERIFY(!null.equals(num));
     QVERIFY(!undefined.equals(num));
 
@@ -3512,18 +3508,18 @@ void tst_QJSValue::engineDeleted()
 
     delete eng;
 
-    QVERIFY(!v1.isValid());
+    QVERIFY(v1.isUndefined());
     QVERIFY(v1.engine() == 0);
-    QVERIFY(!v2.isValid());
+    QVERIFY(v2.isUndefined());
     QVERIFY(v2.engine() == 0);
-    QVERIFY(!v3.isValid());
+    QVERIFY(v3.isUndefined());
     QVERIFY(v3.engine() == 0);
-    QVERIFY(!v4.isValid());
+    QVERIFY(v4.isUndefined());
     QVERIFY(v4.engine() == 0);
-    QVERIFY(v5.isValid());
+    QVERIFY(v5.isString()); // was not bound to engine
     QVERIFY(v5.engine() == 0);
 
-    QVERIFY(!v3.property("foo").isValid());
+    QVERIFY(v3.property("foo").isUndefined());
 }
 
 void tst_QJSValue::valueOfWithClosure()
diff --git a/tests/auto/declarative/qjsvalueiterator/tst_qjsvalueiterator.cpp b/tests/auto/declarative/qjsvalueiterator/tst_qjsvalueiterator.cpp
index f54fcc3918..1965924a09 100644
--- a/tests/auto/declarative/qjsvalueiterator/tst_qjsvalueiterator.cpp
+++ b/tests/auto/declarative/qjsvalueiterator/tst_qjsvalueiterator.cpp
@@ -506,15 +506,15 @@ void tst_QJSValueIterator::iterateOverObjectFromDeletedEngine()
 
     delete engine;
 
-    QVERIFY(!objet.isValid());
+    QVERIFY(objet.isUndefined());
     QVERIFY(it.name().isEmpty());
-    QVERIFY(!it.value().isValid());
+    QVERIFY(it.value().isUndefined());
 
     QVERIFY(!it.hasNext());
     it.next();
 
     QVERIFY(it.name().isEmpty());
-    QVERIFY(!it.value().isValid());
+    QVERIFY(it.value().isUndefined());
 
 }