Ensure that scarce resources work with var properties

Now that we have a new property type which stores JavaScript handles,
we need to ensure that scarce resources can be used with them.

Task-number: QMLNG-18
Task-number: QTBUG-21843
Change-Id: I4a920ae39e7d33cf5e33362e5e0ee21c74cb35e3
Reviewed-by: Martin Jones <martin.jones@nokia.com>

11 files changed, 624 insertions, 136 deletions

diff --git a/doc/src/declarative/basictypes.qdoc b/doc/src/declarative/basictypes.qdoc
index 98eea78a07..a908e73ca8 100644
--- a/doc/src/declarative/basictypes.qdoc
+++ b/doc/src/declarative/basictypes.qdoc
@@ -479,6 +479,19 @@
     }
     \endqml
 
+    A \c var type property can also hold an image or pixmap.
+    A \c var which contains a QPixmap or QImage is known as a
+    "scarce resource" and the declarative engine will attempt to
+    automatically release such resources after evaluation of any JavaScript
+    expression which requires one to be copied has completed.
+
+    Clients may explicitly release such a scarce resource by calling the
+    "destroy" method on the \c var property from within JavaScript.  They
+    may also explicitly preserve the scarce resource by calling the
+    "preserve" method on the \c var property from within JavaScript.
+    For more information regarding the usage of a scarce resource, please
+    see \l{Scarce Resources in JavaScript}.
+
     \sa {QML Basic Types}
 */
 
diff --git a/doc/src/declarative/javascriptblocks.qdoc b/doc/src/declarative/javascriptblocks.qdoc
index a9e383c258..34a1986db6 100644
--- a/doc/src/declarative/javascriptblocks.qdoc
+++ b/doc/src/declarative/javascriptblocks.qdoc
@@ -362,7 +362,7 @@ Item {
 
 \section1 Scarce Resources in JavaScript
 
-As described in the documentation for \l{QML Basic Types}, a \c variant type
+As described in the documentation for \l{QML Basic Types}, a \c var type
 property may hold a "scarce resource" (image or pixmap).  There are several
 important semantics of scarce resources which should be noted:
 
@@ -379,30 +379,12 @@ may be necessary for clients to manually preserve or destroy resources for
 themselves.
 
 For the following examples, imagine that we have defined the following class:
-\code
-class AvatarExample : public QObject
-{
-    Q_OBJECT
-    Q_PROPERTY(QPixmap avatar READ avatar WRITE setAvatar NOTIFY avatarChanged)
-public:
-    AvatarExample(QObject *parent = 0) : QObject(parent), m_value(100, 100) { m_value.fill(Qt::blue); }
-    ~AvatarExample() {}
-
-    QPixmap avatar() const { return m_value; }
-    void setAvatar(QPixmap v) { m_value = v; emit avatarChanged(); }
-
-signals:
-    void avatarChanged();
-
-private:
-    QPixmap m_value;
-};
-\endcode
+
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.h 0
 
 and that we have registered it with the QML type-system as follows:
-\code
-qmlRegisterType<AvatarExample>("Qt.example", 1, 0, "AvatarExample");
-\endcode
+
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.cpp 0
 
 The AvatarExample class has a property which is a pixmap.  When the property
 is accessed in JavaScript scope, a copy of the resource will be created and
@@ -414,141 +396,59 @@ unless the client explicitly preserves it.
 
 \section2 Example One: Automatic Release
 
-In this example, the resource will be automatically
+In the following example, the scarce resource will be automatically released
+after the binding evaluation is complete.
+
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleOne.qml 0
+
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.cpp 1
+
+\section2 Example Two: Automatic Release Prevented By Reference
+
+In this example, the resource will not be automatically
 released after the binding expression evaluation is
-complete.
+complete, because there is a property var referencing the
+scarce resource.
 
-\qml
-// exampleOne.qml
-import QtQuick 1.0
-import Qt.example 1.0
-
-QtObject {
-    property AvatarExample a;
-    a: AvatarExample { id: example }
-    property variant avatar: example.avatar
-}
-\endqml
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleTwo.qml 0
 
-\code
-QDeclarativeComponent component(&engine, "exampleOne.qml");
-QObject *object = component.create();
-// The scarce resource will have been released automatically
-// after the binding expression was evaluated.
-// Since the scarce resource was not released explicitly prior
-// to the binding expression being evaluated, we get the
-// expected result:
-//object->property("scarceResourceCopy").isValid() == true
-delete object;
-\endcode
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.cpp 2
 
-\section2 Example Two: Explicit Preservation
+\section2 Example Three: Explicit Preservation
 
 In this example, the resource must be explicitly preserved in order
 to prevent the declarative engine from automatically releasing the
 resource after evaluation of the imported script.
 
-\code
-// exampleTwo.js
-.import Qt.example 1.0 as QtExample
-
-var component = Qt.createComponent("exampleOne.qml");
-var exampleOneElement = component.createObject(null);
-var avatarExample = exampleOneElement.a;
-var retn = avatarExample.avatar;
-
-// without the following call, the scarce resource held
-// by retn would be automatically released by the engine
-// after the import statement in exampleTwo.qml, prior
-// to the variable assignment.
-retn.preserve();
-
-function importAvatar() {
-    return retn;
-}
-\endcode
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleThree.js 0
 
-\qml
-// exampleTwo.qml
-import QtQuick 1.0
-import Qt.example 1.0
-import "exampleTwo.js" as ExampleTwoJs
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleThree.qml 0
 
-QtObject {
-    property variant avatar: ExampleTwoJs.importAvatar()
-}
-\endqml
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.cpp 3
 
-\code
-QDeclarativeComponent component(&engine, "exampleTwo.qml");
-QObject *object = component.create();
-// The resource was preserved explicitly during evaluation of the
-// JavaScript expression.  Thus, during property assignment, the
-// scarce resource was still valid, and so we get the expected result:
-//object->property("avatar").isValid() == true
-// The scarce resource may not have been cleaned up by the JS GC yet;
-// it will continue to consume system resources until the JS GC runs.
-delete object;
-\endcode
-
-\section2 Example Three: Explicit Destruction
+\section2 Example Four: Explicit Destruction
 
 In the following example, we release (via destroy()) an explicitly preserved
 scarce resource variant.  This example shows how a client may free system
 resources by releasing the scarce resource held in a JavaScript object, if
 required, during evaluation of a JavaScript expression.
 
-\code
-// exampleThree.js
-.import Qt.example 1.0 as QtExample
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFour.js 0
 
-var component = Qt.createComponent("exampleOne.qml");
-var exampleOneElement = component.createObject(null);
-var avatarExample = exampleOneElement.a;
-var retn = avatarExample.avatar;
-retn.preserve();
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFour.qml 0
 
-function importAvatar() {
-    return retn;
-}
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.cpp 4
 
-function releaseAvatar() {
-    retn.destroy();
-}
-\endcode
+\section2 Example Five: Explicit Destruction And JavaScript References
 
-\qml
-// exampleThree.qml
-import QtQuick 1.0
-import Qt.example 1.0
-import "exampleThree.js" as ExampleThreeJs
-
-QtObject {
-    property variant avatarOne
-    property variant avatarTwo
-
-    Component.onCompleted: {
-        avatarOne = ExampleThreeJs.importAvatar(); // valid at this stage
-        ExampleThreeJs.releaseAvatar();            // explicit release
-        avatarTwo = ExampleThreeJs.importAvatar(); // invalid at this stage
-    }
-}
-\endqml
+One thing to be aware of when using "var" type properties is that they
+hold references to JavaScript objects.  As such, if multiple references
+to one scarce resource is held, and the client calls destroy() on one
+of those references (to explicitly release the scarce resource), all of
+the references will be affected.
 
-\code
-QDeclarativeComponent component(&engine, "exampleThree.qml");
-QObject *object = component.create();
-// The scarce resource was explicitly preserved by the client during
-// the evaluation of the imported script, and so the scarce resource
-// remains valid until the explicit call to releaseAvatar().  As such,
-// we get the expected results:
-//object->property("avatarOne").isValid() == true
-//object->property("avatarTwo").isValid() == false
-// Because the scarce resource was released explicitly, it will no longer
-// be consuming any system resources (beyond what a normal JS Object would;
-// that small overhead will exist until the JS GC runs, as per any other
-// JavaScript object).
-delete object;
-\endcode
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFive.qml 0
+
+\snippet doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.cpp 5
 
 */
diff --git a/doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.cpp b/doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.cpp
new file mode 100644
index 0000000000..eb521e1e7e
--- /dev/null
+++ b/doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.cpp
@@ -0,0 +1,124 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
+**     the names of its contributors may be used to endorse or promote
+**     products derived from this software without specific prior written
+**     permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "avatarExample.h"
+#include <QDeclarativeEngine>
+#include <QDeclarativeComponent>
+
+void registerTypes()
+{
+//![0]
+    qmlRegisterType<AvatarExample>("Qt.example", 1, 0, "AvatarExample");
+//![0]
+}
+
+void expectOne()
+{
+//![1]
+QDeclarativeComponent component(&engine, "exampleOne.qml");
+QObject *object = component.create();
+// The scarce resource will have been released automatically
+// by this point, after the binding expression was evaluated.
+delete object;
+//![1]
+}
+
+void expectTwo()
+{
+//![2]
+QDeclarativeComponent component(&engine, "exampleTwo.qml");
+QObject *object = component.create();
+// The scarce resource will not have been released automatically
+// after the binding expression was evaluated.
+// Since the scarce resource was not released explicitly prior
+// to the binding expression being evaluated, we get:
+bool expectedResult = (object->property("avatar").isValid() == true);
+delete object;
+//![2]
+}
+
+void expectThree()
+{
+//![3]
+QDeclarativeComponent component(&engine, "exampleThree.qml");
+QObject *object = component.create();
+// The resource was preserved explicitly during evaluation of the
+// JavaScript expression.  Thus, during property assignment, the
+// scarce resource was still valid, and so we get:
+bool expectedResult = (object->property("avatar").isValid() == true);
+// The scarce resource will not be released until all references to
+// the resource are released, and the JavaScript garbage collector runs.
+delete object;
+//![3]
+}
+
+void expectFour()
+{
+//![4]
+QDeclarativeComponent component(&engine, "exampleFour.qml");
+QObject *object = component.create();
+// The scarce resource was explicitly preserved by the client during
+// the importAvatar() function, and so the scarce resource
+// remains valid until the explicit call to releaseAvatar().  As such,
+// we get the expected results:
+bool expectedResultOne = (object->property("avatarOne").isValid() == true);
+bool expectedResultTwo = (object->property("avatarTwo").isValid() == false);
+// Because the scarce resource referenced by avatarTwo was released explicitly,
+// it will no longer be consuming any system resources (beyond what a normal
+// JS Object would; that small overhead will exist until the JS GC runs, as per
+// any other JavaScript object).
+delete object;
+//![4]
+}
+
+void expectFive()
+{
+//![5]
+QDeclarativeComponent component(&engine, "exampleFive.qml");
+QObject *object = component.create();
+// We have the expected results:
+bool expectedResultOne = (object->property("avatarOne").isValid() == false);
+bool expectedResultTwo = (object->property("avatarTwo").isValid() == false);
+// Because although only avatarTwo was explicitly released,
+// avatarOne and avatarTwo were referencing the same
+// scarce resource.
+delete object;
+//![5]
+}
diff --git a/doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.h b/doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.h
new file mode 100644
index 0000000000..17cef5e5cd
--- /dev/null
+++ b/doc/src/snippets/declarative/integrating-javascript/scarceresources/avatarExample.h
@@ -0,0 +1,73 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
+**     the names of its contributors may be used to endorse or promote
+**     products derived from this software without specific prior written
+**     permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef AVATAREXAMPLE_P_H
+#define AVATAREXAMPLE_P_H
+
+#include <QObject>
+#include <QPixmap>
+
+//![0]
+// avatarExample.h
+class AvatarExample : public QObject
+{
+    Q_OBJECT
+    Q_PROPERTY(QPixmap avatar READ avatar WRITE setAvatar NOTIFY avatarChanged)
+public:
+    AvatarExample(QObject *parent = 0)
+        : QObject(parent), m_value(100, 100)
+    {
+        m_value.fill(Qt::blue);
+    }
+
+    ~AvatarExample() {}
+
+    QPixmap avatar() const { return m_value; }
+    void setAvatar(QPixmap v) { m_value = v; emit avatarChanged(); }
+
+signals:
+    void avatarChanged();
+
+private:
+    QPixmap m_value;
+};
+//![0]
+
+#endif
diff --git a/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFive.qml b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFive.qml
new file mode 100644
index 0000000000..33326b744d
--- /dev/null
+++ b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFive.qml
@@ -0,0 +1,54 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
+**     the names of its contributors may be used to endorse or promote
+**     products derived from this software without specific prior written
+**     permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+// exampleFive.qml
+import QtQuick 2.0
+import Qt.example 1.0
+import "exampleFour.js" as ExampleFourJs // use factory from example four
+
+QtObject {
+    property var avatarOne: ExampleFourJs.importAvatar()
+    property var avatarTwo: avatarOne
+
+    Component.onCompleted: {
+        ExampleFourJs.releaseAvatar(avatarTwo);
+    }
+}
+//![0]
\ No newline at end of file
diff --git a/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFour.js b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFour.js
new file mode 100644
index 0000000000..476e03fdf8
--- /dev/null
+++ b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFour.js
@@ -0,0 +1,56 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
+**     the names of its contributors may be used to endorse or promote
+**     products derived from this software without specific prior written
+**     permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+// exampleFour.js
+.import Qt.example 1.0 as QtExample
+
+function importAvatar() {
+    var component = Qt.createComponent("exampleTwo.qml");
+    var exampleOneElement = component.createObject(null);
+    var avatarExample = exampleOneElement.a;
+    var retn = avatarExample.avatar;
+    retn.preserve();
+    return retn;
+}
+
+function releaseAvatar(avatar) {
+    avatar.destroy();
+}
+//![0]
\ No newline at end of file
diff --git a/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFour.qml b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFour.qml
new file mode 100644
index 0000000000..e423771a20
--- /dev/null
+++ b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleFour.qml
@@ -0,0 +1,56 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
+**     the names of its contributors may be used to endorse or promote
+**     products derived from this software without specific prior written
+**     permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+// exampleFour.qml
+import QtQuick 2.0
+import Qt.example 1.0
+import "exampleFour.js" as ExampleFourJs
+
+QtObject {
+    property var avatarOne
+    property var avatarTwo
+
+    Component.onCompleted: {
+        avatarOne = ExampleFourJs.importAvatar();
+        avatarTwo = ExampleFourJs.importAvatar();
+        ExampleFourJs.releaseAvatar(avatarTwo);
+    }
+}
+//![0]
\ No newline at end of file
diff --git a/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleOne.qml b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleOne.qml
new file mode 100644
index 0000000000..c8579b7c6c
--- /dev/null
+++ b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleOne.qml
@@ -0,0 +1,54 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
+**     the names of its contributors may be used to endorse or promote
+**     products derived from this software without specific prior written
+**     permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+// exampleOne.qml
+import QtQuick 1.0
+import Qt.example 1.0
+
+QtObject {
+    property AvatarExample a;
+    a: AvatarExample { id: example }
+    property var avatarWidth: example.avatar,100
+    // Here, we use "example.avatar,100" purely for illustration.
+    // The value of `avatarWidth' will be 100 after evaluation.
+    // E.g., you could imagine some js function which takes
+    // an avatar, and returns the width of the avatar.
+}
+//![0]
\ No newline at end of file
diff --git a/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleThree.js b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleThree.js
new file mode 100644
index 0000000000..4fefb1e3f7
--- /dev/null
+++ b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleThree.js
@@ -0,0 +1,58 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
+**     the names of its contributors may be used to endorse or promote
+**     products derived from this software without specific prior written
+**     permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+// exampleThree.js
+.import Qt.example 1.0 as QtExample
+
+var component = Qt.createComponent("exampleTwo.qml");
+var exampleOneElement = component.createObject(null);
+var avatarExample = exampleOneElement.a;
+var retn = avatarExample.avatar;
+
+// without the following call, the scarce resource held
+// by retn would be automatically released by the engine
+// after the import statement in exampleTwo.qml, prior
+// to the variable assignment.
+retn.preserve();
+
+function importAvatar() {
+    return retn;
+}
+//![0]
\ No newline at end of file
diff --git a/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleThree.qml b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleThree.qml
new file mode 100644
index 0000000000..58382902c8
--- /dev/null
+++ b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleThree.qml
@@ -0,0 +1,49 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
+**     the names of its contributors may be used to endorse or promote
+**     products derived from this software without specific prior written
+**     permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+// exampleThree.qml
+import QtQuick 1.0
+import Qt.example 1.0
+import "exampleThree.js" as ExampleThreeJs
+
+QtObject {
+    property var avatar: ExampleThreeJs.importAvatar()
+}
+//![0]
\ No newline at end of file
diff --git a/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleTwo.qml b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleTwo.qml
new file mode 100644
index 0000000000..610a75b97f
--- /dev/null
+++ b/doc/src/snippets/declarative/integrating-javascript/scarceresources/exampleTwo.qml
@@ -0,0 +1,51 @@
+/****************************************************************************
+**
+** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
+**     the names of its contributors may be used to endorse or promote
+**     products derived from this software without specific prior written
+**     permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+// exampleTwo.qml
+import QtQuick 1.0
+import Qt.example 1.0
+
+QtObject {
+    property AvatarExample a;
+    a: AvatarExample { id: example }
+    property var avatar: example.avatar
+    // Now `avatar' contains a reference to the scarce resource.
+}
+//![0]
\ No newline at end of file