QScriptEngine Class | Qt Script

Qt 5.14 | Qt Script | C++ Classes | QScriptEngine

Qt 5.14.1 Reference Documentation

# QScriptEngine Class

The QScriptEngine class provides an environment for evaluating Qt Script code. More...

Header: | #include <QScriptEngine>
qmake: | QT += script
Since: | Qt 4.3
Inherits: | QObject

This class was introduced in Qt 4.3.

- List of all members, including inherited members
- Obsolete members

Note: All functions in this class are reentrant.

## Public Types

typedef | FunctionSignature
typedef | FunctionWithArgSignature
enum | QObjectWrapOption { ExcludeChildObjects, ExcludeSuperClassMethods, ExcludeSuperClassProperties, ExcludeSuperClassContents, ExcludeDeleteLater, …, SkipMethodsInEnumeration }
flags | QObjectWrapOptions
enum | ValueOwnership { QtOwnership, ScriptOwnership, AutoOwnership }

## Public Functions

| QScriptEngine(QObject *parent)
| QScriptEngine()
virtual | ~QScriptEngine()
void | abortEvaluation(const QScriptValue &result = QScriptValue())
QScriptEngineAgent * | agent() const
QStringList | availableExtensions() const
void | clearExceptions()
void | collectGarbage()
QScriptContext * | currentContext() const
QScriptValue | defaultPrototype(int metaTypeId) const
QScriptValue | evaluate(const QString &program, const QString &fileName = QString(), int lineNumber = 1)
QScriptValue | evaluate(const QScriptProgram &program)
T | fromScriptValue(const QScriptValue &value)
QScriptValue | globalObject() const
bool | hasUncaughtException() const
QScriptValue | importExtension(const QString &extension)
QStringList | importedExtensions() const
void | installTranslatorFunctions(const QScriptValue &object = QScriptValue())
bool | isEvaluating() const
QScriptValue | newArray(uint length = 0)
QScriptValue | newDate(qsreal value)
QScriptValue | newDate(const QDateTime &value)
QScriptValue | newFunction(QScriptEngine::FunctionSignature fun, int length = 0)
QScriptValue | newFunction(QScriptEngine::FunctionSignature fun, const QScriptValue &prototype, int length = 0)
QScriptValue | newObject()
QScriptValue | newObject(QScriptClass *scriptClass, const QScriptValue &data = QScriptValue())
QScriptValue | newQMetaObject(const QMetaObject *metaObject, const QScriptValue &ctor = QScriptValue())
QScriptValue | newQObject(QObject *object, QScriptEngine::ValueOwnership ownership = QtOwnership, const QScriptEngine::QObjectWrapOptions &options = QObjectWrapOptions())
QScriptValue | newQObject(const QScriptValue &scriptObject, QObject *qtObject, QScriptEngine::ValueOwnership ownership = QtOwnership, const QScriptEngine::QObjectWrapOptions &options = QObjectWrapOptions())
QScriptValue | newRegExp(const QRegExp &regexp)
QScriptValue | newRegExp(const QString &pattern, const QString &flags)
QScriptValue | newVariant(const QVariant &value)
QScriptValue | newVariant(const QScriptValue &object, const QVariant &value)
QScriptValue | nullValue()
void | popContext()
int | processEventsInterval() const
QScriptContext * | pushContext()
void | reportAdditionalMemoryCost(int size)
QScriptValue | scriptValueFromQMetaObject()
void | setAgent(QScriptEngineAgent *agent)
void | setDefaultPrototype(int metaTypeId, const QScriptValue &prototype)
void | setGlobalObject(const QScriptValue &object)
void | setProcessEventsInterval(int interval)
QScriptValue | toObject(const QScriptValue &value)
QScriptValue | toScriptValue(const T &value)
QScriptString | toStringHandle(const QString &str)
QScriptValue | uncaughtException() const
QStringList | uncaughtExceptionBacktrace() const
int | uncaughtExceptionLineNumber() const
QScriptValue | undefinedValue()

## Signals

void | signalHandlerException(const QScriptValue &exception)

## Static Public Members

QScriptSyntaxCheckResult | checkSyntax(const QString &program)

## Related Non-Members

bool | qScriptConnect(QObject *sender, const char *signal, const QScriptValue &receiver, const QScriptValue &function)
bool | qScriptDisconnect(QObject *sender, const char *signal, const QScriptValue &receiver, const QScriptValue &function)
int | qScriptRegisterMetaType(QScriptEngine *eng, QScriptValue (*)(QScriptEngine *, const T &) toScriptValue, void (*)(const QScriptValue &, T &) fromScriptValue, const QScriptValue &prototype = QScriptValue(), T * = 0)
int | qScriptRegisterSequenceMetaType(QScriptEngine *engine, const QScriptValue &prototype = QScriptValue(), T * = 0)
QScriptValue | qScriptValueFromSequence(QScriptEngine *engine, const Container &container)
void | qScriptValueToSequence(const QScriptValue &value, Container &container)

## Macros

| Q_SCRIPT_DECLARE_QMETAOBJECT(QMetaObject, ArgType)

## Detailed Description

See the Qt Script documentation for information about the Qt Script language, and how to get started with scripting your C++ application.

### Evaluating Scripts

Use evaluate() to evaluate script code; this is the C++ equivalent of the built-in script function `eval()`.

      QScriptEngine myEngine;
      QScriptValue three = myEngine.evaluate("1 + 2");

evaluate() returns a QScriptValue that holds the result of the evaluation. The QScriptValue class provides functions for converting the result to various C++ types (e.g. QScriptValue::toString() and QScriptValue::toNumber()).

The following code snippet shows how a script function can be defined and then invoked from C++ using QScriptValue::call():

      QScriptValue fun = myEngine.evaluate("(function(a, b) { return a + b; })");
      QScriptValueList args;
      args << 1 << 2;
      QScriptValue threeAgain = fun.call(QScriptValue(), args);

As can be seen from the above snippets, a script is provided to the engine in the form of a string. One common way of loading scripts is by reading the contents of a file and passing it to evaluate():

      QString fileName = "helloworld.qs";
      QFile scriptFile(fileName);
      if (!scriptFile.open(QIODevice::ReadOnly))
          // handle error
      QTextStream stream(&scriptFile);
      QString contents = stream.readAll();
      scriptFile.close();
      myEngine.evaluate(contents, fileName);

Here we pass the name of the file as the second argument to evaluate(). This does not affect evaluation in any way; the second argument is a general-purpose string that is used to identify the script for debugging purposes (for example, our filename will now show up in any uncaughtExceptionBacktrace() involving the script).

### Engine Configuration

The globalObject() function returns the Global Object associated with the script engine. Properties of the Global Object are accessible from any script code (i.e. they are global variables). Typically, before evaluating "user" scripts, you will want to configure a script engine by adding one or more properties to the Global Object:

      myEngine.globalObject().setProperty("myNumber", 123);
      ...
      QScriptValue myNumberPlusOne = myEngine.evaluate("myNumber + 1");

Adding custom properties to the scripting environment is one of the standard means of providing a scripting API that is specific to your application. Usually these custom properties are objects created by the newQObject() or newObject() functions, or constructor functions created by newFunction().

### Script Exceptions

evaluate() can throw a script exception (e.g. due to a syntax error); in that case, the return value is the value that was thrown (typically an `Error` object). You can check whether the evaluation caused an exception by calling hasUncaughtException(). In that case, you can call toString() on the error object to obtain an error message. The current uncaught exception is also available through uncaughtException(). Calling clearExceptions() will cause any uncaught exceptions to be cleared.

      QScriptValue result = myEngine.evaluate(...);
      if (myEngine.hasUncaughtException()) {
          int line = myEngine.uncaughtExceptionLineNumber();
          qDebug() << "uncaught exception at line" << line << ":" << result.toString();
      }

The checkSyntax() function can be used to determine whether code can be usefully passed to evaluate().

### Script Object Creation

Use newObject() to create a standard Qt Script object; this is the C++ equivalent of the script statement `new Object()`. You can use the object-specific functionality in QScriptValue to manipulate the script object (e.g. QScriptValue::setProperty()). Similarly, use newArray() to create a Qt Script array object. Use newDate() to create a `Date` object, and newRegExp() to create a `RegExp` object.

### QObject Integration

Use newQObject() to wrap a QObject (or subclass) pointer. newQObject() returns a proxy script object; properties, children, and signals and slots of the QObject are available as properties of the proxy object. No binding code is needed because it is done dynamically using the Qt meta object system.

      QPushButton button;
      QScriptValue scriptButton = myEngine.newQObject(&button);
      myEngine.globalObject().setProperty("button", scriptButton);

      myEngine.evaluate("button.checkable = true");

      qDebug() << scriptButton.property("checkable").toBoolean();
      scriptButton.property("show").call(); // call the show() slot

Use qScriptConnect() to connect a C++ signal to a script function; this is the Qt Script equivalent of QObject::connect(). When a script function is invoked in response to a C++ signal, it can cause a script exception; you can connect to the signalHandlerException() signal to catch such an exception.

Use newQMetaObject() to wrap a QMetaObject; this gives you a "script representation" of a QObject-based class. newQMetaObject() returns a proxy script object; enum values of the class are available as properties of the proxy object. You can also specify a function that will be used to construct objects of the class (e.g. when the constructor is invoked from a script). For classes that have a "standard" Qt constructor, Qt Script can provide a default script constructor for you; see scriptValueFromQMetaObject().

See Making Applications Scriptable for more information on the QObject integration.

### Support for Custom C++ Types

Use newVariant() to wrap a QVariant. This can be used to store values of custom (non-QObject) C++ types that have been registered with the Qt meta-type system. To make such types scriptable, you typically associate a prototype (delegate) object with the C++ type by calling setDefaultPrototype(); the prototype object defines the scripting API for the C++ type. Unlike the QObject integration, there is no automatic binding possible here; i.e. you have to create the scripting API yourself, for example by using the QScriptable class.

Use fromScriptValue() to cast from a QScriptValue to another type, and toScriptValue() to create a QScriptValue from another value. You can specify how the conversion of C++ types is to be performed with qScriptRegisterMetaType() and qScriptRegisterSequenceMetaType(). By default, Qt Script will use QVariant to store values of custom types.

### Importing Extensions

Use importExtension() to import plugin-based extensions into the engine. Call availableExtensions() to obtain a list naming all the available extensions, and importedExtensions() to obtain a list naming only those extensions that have been imported.

Call pushContext() to open up a new variable scope, and popContext() to close the current scope. This is useful if you are implementing an extension that evaluates script code containing temporary variable definitions (e.g. `var foo = 123;`) that are safe to discard when evaluation has completed.

### Native Functions

Use newFunction() to wrap native (C++) functions, including constructors for your own custom types, so that these can be invoked from script code. Such functions must have the signature QScriptEngine::FunctionSignature. You may then pass the function as argument to newFunction(). Here is an example of a function that returns the sum of its first two arguments:

      QScriptValue myAdd(QScriptContext *context, QScriptEngine *engine)
      {
         QScriptValue a = context->argument(0);
         QScriptValue b = context->argument(1);
         return a.toNumber() + b.toNumber();
      }

To expose this function to script code, you can set it as a property of the Global Object:

      QScriptValue fun = myEngine.newFunction(myAdd);
      myEngine.globalObject().setProperty("myAdd", fun);

Once this is done, script code can call your function in the exact same manner as a "normal" script function:

      QScriptValue result = myEngine.evaluate("myAdd(myNumber, 1)");

### Long-running Scripts

If you need to evaluate possibly long-running scripts from the main (GUI) thread, you should first call setProcessEventsInterval() to make sure that the GUI stays responsive. You can abort a currently running script by calling abortEvaluation(). You can determine whether an engine is currently running a script by calling isEvaluating().

### Garbage Collection

Qt Script objects may be garbage collected when they are no longer referenced. There is no guarantee as to when automatic garbage collection will take place.

The collectGarbage() function can be called to explicitly request garbage collection.

The reportAdditionalMemoryCost() function can be called to indicate that a Qt Script object occupies memory that isn't managed by the scripting environment. Reporting the additional cost makes it more likely that the garbage collector will be triggered. This can be useful, for example, when many custom, native Qt Script objects are allocated.

### Core Debugging/Tracing Facilities

Since Qt 4.4, you can be notified of events pertaining to script execution (e.g. script function calls and statement execution) through the QScriptEngineAgent interface; see the setAgent() function. This can be used to implement debugging and profiling of a QScriptEngine.

See also QScriptValue, QScriptContext, and QScriptEngineAgent.

## Member Type Documentation

### typedef QScriptEngine::FunctionSignature

The function signature `QScriptValue f(QScriptContext *, QScriptEngine *)`.

A function with such a signature can be passed to QScriptEngine::newFunction() to wrap the function.

### typedef QScriptEngine::FunctionWithArgSignature

The function signature `QScriptValue f(QScriptContext *, QScriptEngine *, void *)`.

A function with such a signature can be passed to QScriptEngine::newFunction() to wrap the function.

### enum QScriptEngine::QObjectWrapOption
flags QScriptEngine::QObjectWrapOptions

These flags specify options when wrapping a QObject pointer with newQObject().

Constant | Value | Description
--- | --- | ---
`QScriptEngine::ExcludeChildObjects` | `0x0001` | The script object will not expose child objects as properties.
`QScriptEngine::ExcludeSuperClassMethods` | `0x0002` | The script object will not expose signals and slots inherited from the superclass.
`QScriptEngine::ExcludeSuperClassProperties` | `0x0004` | The script object will not expose properties inherited from the superclass.
`QScriptEngine::ExcludeSuperClassContents` | `0x0006` | Shorthand form for ExcludeSuperClassMethods | ExcludeSuperClassProperties
`QScriptEngine::ExcludeDeleteLater` | `0x0010` | The script object will not expose the QObject::deleteLater() slot.
`QScriptEngine::ExcludeSlots` | `0x0020` | The script object will not expose the QObject's slots.
`QScriptEngine::AutoCreateDynamicProperties` | `0x0100` | Properties that don't already exist in the QObject will be created as dynamic properties of that object, rather than as properties of the script object.
`QScriptEngine::PreferExistingWrapperObject` | `0x0200` | If a wrapper object with the requested configuration already exists, return that object.
`QScriptEngine::SkipMethodsInEnumeration` | `0x0008` | Don't include methods (signals and slots) when enumerating the object's properties.

The QObjectWrapOptions type is a typedef for QFlags<QObjectWrapOption>. It stores an OR combination of QObjectWrapOption values.

### enum QScriptEngine::ValueOwnership

This enum specifies the ownership when wrapping a C++ value, e.g. by using newQObject().

Constant | Value | Description
--- | --- | ---
`QScriptEngine::QtOwnership` | `0` | The standard Qt ownership rules apply, i.e. the associated object will never be explicitly deleted by the script engine. This is the default. (QObject ownership is explained in Object Trees & Ownership.)
`QScriptEngine::ScriptOwnership` | `1` | The value is owned by the script environment. The associated data will be deleted when appropriate (i.e. after the garbage collector has discovered that there are no more live references to the value).
`QScriptEngine::AutoOwnership` | `2` | If the associated object has a parent, the Qt ownership rules apply (QtOwnership); otherwise, the object is owned by the script environment (ScriptOwnership).

## Member Function Documentation

### QScriptEngine::QScriptEngine(QObject *parent)

Constructs a QScriptEngine object with the given parent.

The globalObject() is initialized to have properties as described in ECMA-262, Section 15.1.

### QScriptEngine::QScriptEngine()

Constructs a QScriptEngine object.

The globalObject() is initialized to have properties as described in ECMA-262, Section 15.1.

### `[signal]` void QScriptEngine::signalHandlerException(const QScriptValue &exception)

This signal is emitted when a script function connected to a signal causes an exception.

This function was introduced in Qt 4.4.

See also qScriptConnect().

### `[virtual]` QScriptEngine::~QScriptEngine()

Destroys this QScriptEngine.

### void QScriptEngine::abortEvaluation(const QScriptValue &result = QScriptValue())

Aborts any script evaluation currently taking place in this engine. The given result is passed back as the result of the evaluation (i.e. it is returned from the call to evaluate() being aborted).

If the engine isn't evaluating a script (i.e. isEvaluating() returns false), this function does nothing.

Call this function if you need to abort a running script for some reason, e.g. when you have detected that the script has been running for several seconds without completing.

This function was introduced in Qt 4.4.

See also evaluate(), isEvaluating(), and setProcessEventsInterval().

### QScriptEngineAgent *QScriptEngine::agent() const

Returns the agent currently installed on this engine, or 0 if no agent is installed.

This function was introduced in Qt 4.4.

See also setAgent().

### QStringList QScriptEngine::availableExtensions() const

Returns a list naming the available extensions that can be imported using the importExtension() function. This list includes extensions that have been imported.

This function was introduced in Qt 4.4.

See also importExtension() and importedExtensions().

### `[static]` QScriptSyntaxCheckResult QScriptEngine::checkSyntax(const QString &program)

Checks the syntax of the given program. Returns a QScriptSyntaxCheckResult object that contains the result of the check.

This function was introduced in Qt 4.5.

### void QScriptEngine::clearExceptions()

Clears any uncaught exceptions in this engine.

This function was introduced in Qt 4.4.

See also hasUncaughtException().

### void QScriptEngine::collectGarbage()

Runs the garbage collector.

The garbage collector will attempt to reclaim memory by locating and disposing of objects that are no longer reachable in the script environment.

Normally you don't need to call this function; the garbage collector will automatically be invoked when the QScriptEngine decides that it's wise to do so (i.e. when a certain number of new objects have been created). However, you can call this function to explicitly request that garbage collection should be performed as soon as possible.

See also reportAdditionalMemoryCost().

### QScriptContext *QScriptEngine::currentContext() const

Returns the current context.

The current context is typically accessed to retrieve the arguments and `this' object in native functions; for convenience, it is available as the first argument in QScriptEngine::FunctionSignature.

### QScriptValue QScriptEngine::defaultPrototype(int metaTypeId) const

Returns the default prototype associated with the given metaTypeId, or an invalid QScriptValue if no default prototype has been set.

See also setDefaultPrototype().

### QScriptValue QScriptEngine::evaluate(const QString &program, const QString &fileName = QString(), int lineNumber = 1)

Evaluates program, using lineNumber as the base line number, and returns the result of the evaluation.

The script code will be evaluated in the current context.

The evaluation of program can cause an exception in the engine; in this case the return value will be the exception that was thrown (typically an `Error` object). You can call hasUncaughtException() to determine if an exception occurred in the last call to evaluate().

lineNumber is used to specify a starting line number for program; line number information reported by the engine that pertain to this evaluation (e.g. uncaughtExceptionLineNumber()) will be based on this argument. For example, if program consists of two lines of code, and the statement on the second line causes a script exception, uncaughtExceptionLineNumber() would return the given lineNumber plus one. When no starting line number is specified, line numbers will be 1-based.

fileName is used for error reporting. For example in error objects the file name is accessible through the "fileName" property if it's provided with this function.

See also canEvaluate(), hasUncaughtException(), isEvaluating(), and abortEvaluation().

### QScriptValue QScriptEngine::evaluate(const QScriptProgram &program)

Evaluates the given program and returns the result of the evaluation.

This function was introduced in Qt 4.7.

### T QScriptEngine::fromScriptValue(const QScriptValue &value)

Returns the given value converted to the template type `T`.

Note that `T` must be known to QMetaType.

See Conversion Between Qt Script and C++ Types for a description of the built-in type conversion provided by Qt Script.

See also toScriptValue() and qScriptRegisterMetaType().

### QScriptValue QScriptEngine::globalObject() const

Returns this engine's Global Object.

By default, the Global Object contains the built-in objects that are part of ECMA-262, such as Math, Date and String. Additionally, you can set properties of the Global Object to make your own extensions available to all script code. Non-local variables in script code will be created as properties of the Global Object, as well as local variables in global code.

See also setGlobalObject().

### bool QScriptEngine::hasUncaughtException() const

Returns true if the last script evaluation resulted in an uncaught exception; otherwise returns false.

The exception state is cleared when evaluate() is called.

See also uncaughtException() and uncaughtExceptionLineNumber().

### QScriptValue QScriptEngine::importExtension(const QString &extension)

Imports the given extension into this QScriptEngine. Returns undefinedValue() if the extension was successfully imported. You can call hasUncaughtException() to check if an error occurred; in that case, the return value is the value that was thrown by the exception (usually an `Error` object).

QScriptEngine ensures that a particular extension is only imported once; subsequent calls to importExtension() with the same extension name will do nothing and return undefinedValue().

See also availableExtensions(), QScriptExtensionPlugin, and Creating Qt Script Extensions.

### QStringList QScriptEngine::importedExtensions() const

Returns a list naming the extensions that have been imported using the importExtension() function.

This function was introduced in Qt 4.4.

See also availableExtensions().

### void QScriptEngine::installTranslatorFunctions(const QScriptValue &object = QScriptValue())

Installs translator functions on the given object, or on the Global Object if no object is specified.

The relation between Qt Script translator functions and C++ translator functions is described in the following table:

Script Function | Corresponding C++ Function
--- | ---
qsTr() | QObject::tr()
QT_TR_NOOP() | QT_TR_NOOP()
qsTranslate() | QCoreApplication::translate()
QT_TRANSLATE_NOOP() | QT_TRANSLATE_NOOP()
qsTrId() (since 4.7) | qtTrId()
QT_TRID_NOOP() (since 4.7) | QT_TRID_NOOP()

This function was introduced in Qt 4.5.

See also Internationalization with Qt.

### bool QScriptEngine::isEvaluating() const

Returns true if this engine is currently evaluating a script, otherwise returns false.

This function was introduced in Qt 4.4.

See also evaluate() and abortEvaluation().

### QScriptValue QScriptEngine::newArray(uint length = 0)

Creates a Qt Script object of class Array with the given length.

See also newObject().

### QScriptValue QScriptEngine::newDate(qsreal value)

Creates a Qt Script object of class Date with the given value (the number of milliseconds since 01 January 1970, UTC).

### QScriptValue QScriptEngine::newDate(const QDateTime &value)

Creates a Qt Script object of class Date from the given value.

See also QScriptValue::toDateTime().

### QScriptValue QScriptEngine::newFunction(QScriptEngine::FunctionSignature fun, int length = 0)

Creates a QScriptValue that wraps a native (C++) function. fun must be a C++ function with signature QScriptEngine::FunctionSignature. length is the number of arguments that fun expects; this becomes the `length` property of the created QScriptValue.

Note that length only gives an indication of the number of arguments that the function expects; an actual invocation of a function can include any number of arguments. You can check the argumentCount() of the QScriptContext associated with the invocation to determine the actual number of arguments passed.

A `prototype` property is automatically created for the resulting function object, to provide for the possibility that the function will be used as a constructor.

By combining newFunction() and the property flags QScriptValue::PropertyGetter and QScriptValue::PropertySetter, you can create script object properties that behave like normal properties in script code, but are in fact accessed through functions (analogous to how properties work in Qt's Property System). Example:

      static QScriptValue getSetFoo(QScriptContext *context, QScriptEngine *engine)
      {
          QScriptValue callee = context->callee();
          if (context->argumentCount() == 1) // writing?
              callee.setProperty("value", context->argument(0));
          return callee.property("value");
      }

      ....

      QScriptValue object = engine.newObject();
      object.setProperty("foo", engine.newFunction(getSetFoo),
          QScriptValue::PropertyGetter | QScriptValue::PropertySetter);

When the property `foo` of the script object is subsequently accessed in script code, `getSetFoo()` will be invoked to handle the access. In this particular case, we chose to store the "real" value of `foo` as a property of the accessor function itself; you are of course free to do whatever you like in this function.

In the above example, a single native function was used to handle both reads and writes to the property; the argument count is used to determine if we are handling a read or write. You can also use two separate functions; just specify the relevant flag (QScriptValue::PropertyGetter or QScriptValue::PropertySetter) when setting the property, e.g.:

      QScriptValue object = engine.newObject();
      object.setProperty("foo", engine.newFunction(getFoo), QScriptValue::PropertyGetter);
      object.setProperty("foo", engine.newFunction(setFoo), QScriptValue::PropertySetter);

See also QScriptValue::call().

### QScriptValue QScriptEngine::newFunction(QScriptEngine::FunctionSignature fun, const QScriptValue &prototype, int length = 0)

Creates a constructor function from fun, with the given length. The `prototype` property of the resulting function is set to be the given prototype. The `constructor` property of prototype is set to be the resulting function.

When a function is called as a constructor (e.g. `new Foo()`), the `this' object associated with the function call is the new object that the function is expected to initialize; the prototype of this default constructed object will be the function's public `prototype` property. If you always want the function to behave as a constructor (e.g. `Foo()` should also create a new object), or if you need to create your own object rather than using the default `this' object, you should make sure that the prototype of your object is set correctly; either by setting it manually, or, when wrapping a custom type, by having registered the defaultPrototype() of that type. Example:

      QScriptValue Foo(QScriptContext *context, QScriptEngine *engine)
      {
          if (context->calledAsConstructor()) {
              // initialize the new object
              context->thisObject().setProperty("bar", ...);
              // ...
              // return a non-object value to indicate that the
              // thisObject() should be the result of the "new Foo()" expression
              return engine->undefinedValue();
          } else {
              // not called as "new Foo()", just "Foo()"
              // create our own object and return that one
              QScriptValue object = engine->newObject();
              object.setPrototype(context->callee().property("prototype"));
              object.setProperty("baz", ...);
              return object;
          }
      }

      ...

      QScriptValue fooProto = engine->newObject();
      fooProto.setProperty("whatever", ...);
      engine->globalObject().setProperty("Foo", engine->newFunction(Foo, fooProto));

To wrap a custom type and provide a constructor for it, you'd typically do something like this:

      class Bar { ... };

      Q_DECLARE_METATYPE(Bar)

      QScriptValue constructBar(QScriptContext *context, QScriptEngine *engine)
      {
          Bar bar;
          // initialize from arguments in context, if desired
          ...
          return engine->toScriptValue(bar);
      }

      class BarPrototype : public QObject, public QScriptable
      {
      // provide the scriptable interface of this type using slots and properties
      ...
      };

      ...

      // create and register the Bar prototype and constructor in the engine
      BarPrototype *barPrototypeObject = new BarPrototype(...);
      QScriptValue barProto = engine->newQObject(barPrototypeObject);
      engine->setDefaultPrototype(qMetaTypeId<Bar>, barProto);
      QScriptValue barCtor = engine->newFunction(constructBar, barProto);
      engine->globalObject().setProperty("Bar", barCtor);

### QScriptValue QScriptEngine::newObject()

Creates a Qt Script object of class Object.

The prototype of the created object will be the Object prototype object.

See also newArray() and QScriptValue::setProperty().

### QScriptValue QScriptEngine::newObject(QScriptClass *scriptClass, const QScriptValue &data = QScriptValue())

This is an overloaded function.

Creates a Qt Script Object of the given class, scriptClass.

The prototype of the created object will be the Object prototype object.

data, if specified, is set as the internal data of the new object (using QScriptValue::setData()).

This function was introduced in Qt 4.4.

See also QScriptValue::scriptClass() and reportAdditionalMemoryCost().

### QScriptValue QScriptEngine::newQMetaObject(const QMetaObject *metaObject, const QScriptValue &ctor = QScriptValue())

Creates a Qt Script object that represents a QObject class, using the the given metaObject and constructor ctor.

Enums of metaObject (declared with Q_ENUMS) are available as properties of the created QScriptValue. When the class is called as a function, ctor will be called to create a new instance of the class.

Example:

      QScriptValue mySpecialQObjectConstructor(QScriptContext *context,
                                               QScriptEngine *engine)
      {
          QObject *parent = context->argument(0).toQObject();
          QObject *object = new QObject(parent);
          return engine->newQObject(object, QScriptEngine::ScriptOwnership);
      }

      ...

      QScriptValue ctor = engine.newFunction(mySpecialQObjectConstructor);
      QScriptValue metaObject = engine.newQMetaObject(&QObject::staticMetaObject, ctor);
      engine.globalObject().setProperty("QObject", metaObject);

      QScriptValue result = engine.evaluate("new QObject()");

See also newQObject() and scriptValueFromQMetaObject().

### QScriptValue QScriptEngine::newQObject(QObject *object, QScriptEngine::ValueOwnership ownership = QtOwnership, const QScriptEngine::QObjectWrapOptions &options = QObjectWrapOptions())

Creates a Qt Script object that wraps the given QObject object, using the given ownership. The given options control various aspects of the interaction with the resulting script object.

Signals and slots, properties and children of object are available as properties of the created QScriptValue. For more information, see the Qt Script documentation.

If object is a null pointer, this function returns nullValue().

If a default prototype has been registered for the object's class (or its superclass, recursively), the prototype of the new script object will be set to be that default prototype.

If the given object is deleted outside of Qt Script's control, any attempt to access the deleted QObject's members through the Qt Script wrapper object (either by script code or C++) will result in a script exception.

See also QScriptValue::toQObject() and reportAdditionalMemoryCost().

### QScriptValue QScriptEngine::newQObject(const QScriptValue &scriptObject, QObject *qtObject, QScriptEngine::ValueOwnership ownership = QtOwnership, const QScriptEngine::QObjectWrapOptions &options = QObjectWrapOptions())

This is an overloaded function.

Initializes the given scriptObject to hold the given qtObject, and returns the scriptObject.

This function enables you to "promote" a plain Qt Script object (created by the newObject() function) to a QObject proxy, or to replace the QObject contained inside an object previously created by the newQObject() function.

The prototype() of the scriptObject will remain unchanged.

If scriptObject is not an object, this function behaves like the normal newQObject(), i.e. it creates a new script object and returns it.

This function is useful when you want to provide a script constructor for a QObject-based class. If your constructor is invoked in a `new` expression (QScriptContext::isCalledAsConstructor() returns true), you can pass QScriptContext::thisObject() (the default constructed script object) to this function to initialize the new object.

This function was introduced in Qt 4.4.

See also reportAdditionalMemoryCost().

### QScriptValue QScriptEngine::newRegExp(const QRegExp &regexp)

Creates a Qt Script object of class RegExp with the given regexp.

See also QScriptValue::toRegExp().

### QScriptValue QScriptEngine::newRegExp(const QString &pattern, const QString &flags)

Creates a Qt Script object of class RegExp with the given pattern and flags.

The legal flags are 'g' (global), 'i' (ignore case), and 'm' (multiline).

### QScriptValue QScriptEngine::newVariant(const QVariant &value)

Creates a Qt Script object holding the given variant value.

If a default prototype has been registered with the meta type id of value, then the prototype of the created object will be that prototype; otherwise, the prototype will be the Object prototype object.

See also setDefaultPrototype(), QScriptValue::toVariant(), and reportAdditionalMemoryCost().

### QScriptValue QScriptEngine::newVariant(const QScriptValue &object, const QVariant &value)

This is an overloaded function.

Initializes the given Qt Script object to hold the given variant value, and returns the object.

This function enables you to "promote" a plain Qt Script object (created by the newObject() function) to a variant, or to replace the variant contained inside an object previously created by the newVariant() function.

The prototype() of the object will remain unchanged.

If object is not an object, this function behaves like the normal newVariant(), i.e. it creates a new script object and returns it.

This function is useful when you want to provide a script constructor for a C++ type. If your constructor is invoked in a `new` expression (QScriptContext::isCalledAsConstructor() returns true), you can pass QScriptContext::thisObject() (the default constructed script object) to this function to initialize the new object.

This function was introduced in Qt 4.4.

See also reportAdditionalMemoryCost().

### QScriptValue QScriptEngine::nullValue()

Returns a QScriptValue of the primitive type Null.

See also undefinedValue().

### void QScriptEngine::popContext()

Pops the current execution context and restores the previous one. This function must be used in conjunction with pushContext().

See also pushContext().

### int QScriptEngine::processEventsInterval() const

Returns the interval in milliseconds between calls to QCoreApplication::processEvents() while the interpreter is running.

See also setProcessEventsInterval().

### QScriptContext *QScriptEngine::pushContext()

Enters a new execution context and returns the associated QScriptContext object.

Once you are done with the context, you should call popContext() to restore the old context.

By default, the `this' object of the new context is the Global Object. The context's callee() will be invalid.

This function is useful when you want to evaluate script code as if it were the body of a function. You can use the context's activationObject() to initialize local variables that will be available to scripts. Example:

      QScriptEngine engine;
      QScriptContext *context = engine.pushContext();
      context->activationObject().setProperty("myArg", 123);
      engine.evaluate("var tmp = myArg + 42");
      ...
      engine.popContext();

In the above example, the new variable "tmp" defined in the script will be local to the context; in other words, the script doesn't have any effect on the global environment.

Returns 0 in case of stack overflow

See also popContext().

### void QScriptEngine::reportAdditionalMemoryCost(int size)

Reports an additional memory cost of the given size, measured in bytes, to the garbage collector.

This function can be called to indicate that a Qt Script object has memory associated with it that isn't managed by Qt Script itself. Reporting the additional cost makes it more likely that the garbage collector will be triggered.

Note that if the additional memory is shared with objects outside the scripting environment, the cost should not be reported, since collecting the Qt Script object would not cause the memory to be freed anyway.

Negative size values are ignored, i.e. this function can't be used to report that the additional memory has been deallocated.

This function was introduced in Qt 4.7.

See also collectGarbage().

### QScriptValue QScriptEngine::scriptValueFromQMetaObject()

Creates a QScriptValue that represents the Qt class `T`.

This function is used in combination with one of the Q_SCRIPT_DECLARE_QMETAOBJECT() macro. Example:

      Q_SCRIPT_DECLARE_QMETAOBJECT(QLineEdit, QWidget*)

      ...

      QScriptValue lineEditClass = engine.scriptValueFromQMetaObject<QLineEdit>();
      engine.globalObject().setProperty("QLineEdit", lineEditClass);

See also QScriptEngine::newQMetaObject().

### void QScriptEngine::setAgent(QScriptEngineAgent *agent)

Installs the given agent on this engine. The agent will be notified of various events pertaining to script execution. This is useful when you want to find out exactly what the engine is doing, e.g. when evaluate() is called. The agent interface is the basis of tools like debuggers and profilers.

The engine maintains ownership of the agent.

Calling this function will replace the existing agent, if any.

This function was introduced in Qt 4.4.

See also agent().

### void QScriptEngine::setDefaultPrototype(int metaTypeId, const QScriptValue &prototype)

Sets the default prototype of the C++ type identified by the given metaTypeId to prototype.

The default prototype provides a script interface for values of type metaTypeId when a value of that type is accessed from script code. Whenever the script engine (implicitly or explicitly) creates a QScriptValue from a value of type metaTypeId, the default prototype will be set as the QScriptValue's prototype.

The prototype object itself may be constructed using one of two principal techniques; the simplest is to subclass QScriptable, which enables you to define the scripting API of the type through QObject properties and slots. Another possibility is to create a script object by calling newObject(), and populate the object with the desired properties (e.g. native functions wrapped with newFunction()).

See also defaultPrototype(), qScriptRegisterMetaType(), QScriptable, and Default Prototypes Example.

### void QScriptEngine::setGlobalObject(const QScriptValue &object)

Sets this engine's Global Object to be the given object. If object is not a valid script object, this function does nothing.

When setting a custom global object, you may want to use QScriptValueIterator to copy the properties of the standard Global Object; alternatively, you can set the internal prototype of your custom object to be the original Global Object.

This function was introduced in Qt 4.5.

See also globalObject().

### void QScriptEngine::setProcessEventsInterval(int interval)

Sets the interval between calls to QCoreApplication::processEvents to interval milliseconds.

While the interpreter is running, all event processing is by default blocked. This means for instance that the gui will not be updated and timers will not be fired. To allow event processing during interpreter execution one can specify the processing interval to be a positive value, indicating the number of milliseconds between each time QCoreApplication::processEvents() is called.

The default value is -1, which disables event processing during interpreter execution.

You can use QCoreApplication::postEvent() to post an event that performs custom processing at the next interval. For example, you could keep track of the total running time of the script and call abortEvaluation() when you detect that the script has been running for a long time without completing.

See also processEventsInterval().

### QScriptValue QScriptEngine::toObject(const QScriptValue &value)

Converts the given value to an object, if such a conversion is possible; otherwise returns an invalid QScriptValue. The conversion is performed according to the following table:

Input Type | Result
--- | ---
Undefined | An invalid QScriptValue.
Null | An invalid QScriptValue.
Boolean | A new Boolean object whose internal value is set to the value of the boolean.
Number | A new Number object whose internal value is set to the value of the number.
String | A new String object whose internal value is set to the value of the string.
Object | The result is the object itself (no conversion).

This function was introduced in Qt 4.5.

See also newObject().

### QScriptValue QScriptEngine::toScriptValue(const T &value)

Creates a QScriptValue with the given value.

Note that the template type `T` must be known to QMetaType.

See Conversion Between Qt Script and C++ Types for a description of the built-in type conversion provided by Qt Script. By default, the types that are not specially handled by Qt Script are represented as QVariants (e.g. the value is passed to newVariant()); you can change this behavior by installing your own type conversion functions with qScriptRegisterMetaType().

See also fromScriptValue() and qScriptRegisterMetaType().

### QScriptString QScriptEngine::toStringHandle(const QString &str)

Returns a handle that represents the given string, str.

QScriptString can be used to quickly look up properties, and compare property names, of script objects.

This function was introduced in Qt 4.4.

See also QScriptValue::property().

### QScriptValue QScriptEngine::uncaughtException() const

Returns the current uncaught exception, or an invalid QScriptValue if there is no uncaught exception.

The exception value is typically an `Error` object; in that case, you can call toString() on the return value to obtain an error message.

See also hasUncaughtException() and uncaughtExceptionLineNumber().

### QStringList QScriptEngine::uncaughtExceptionBacktrace() const

Returns a human-readable backtrace of the last uncaught exception.

It is in the form `<function-name>() at <file-name>:<line-number>`.

See also uncaughtException().

### int QScriptEngine::uncaughtExceptionLineNumber() const

Returns the line number where the last uncaught exception occurred.

Line numbers are 1-based, unless a different base was specified as the second argument to evaluate().

See also hasUncaughtException().

### QScriptValue QScriptEngine::undefinedValue()

Returns a QScriptValue of the primitive type Undefined.

See also nullValue().

## Related Non-Members

### bool qScriptConnect(QObject *sender, const char *signal, const QScriptValue &receiver, const QScriptValue &function)

Creates a connection from the signal in the sender to the given function. If receiver is an object, it will act as the `this' object when the signal handler function is invoked. Returns true if the connection succeeds; otherwise returns false.

This function was introduced in Qt 4.4.

See also qScriptDisconnect() and QScriptEngine::signalHandlerException().

### bool qScriptDisconnect(QObject *sender, const char *signal, const QScriptValue &receiver, const QScriptValue &function)

Disconnects the signal in the sender from the given (receiver, function) pair. Returns true if the connection is successfully broken; otherwise returns false.

This function was introduced in Qt 4.4.

See also qScriptConnect().

### int qScriptRegisterMetaType(QScriptEngine *eng, QScriptValue (*)(QScriptEngine *, const T &) toScriptValue, void (*)(const QScriptValue &, T &) fromScriptValue, const QScriptValue &prototype = QScriptValue(), T * = 0)

Registers the type `T` in the given eng. toScriptValue must be a function that will convert from a value of type `T` to a QScriptValue, and fromScriptValue a function that does the opposite. prototype, if valid, is the prototype that's set on QScriptValues returned by toScriptValue.

Returns the internal ID used by QMetaType.

You only need to call this function if you want to provide custom conversion of values of type `T`, i.e. if the default QVariant-based representation and conversion is not appropriate. (Note that custom QObject-derived types also fall in this category; e.g. for a QObject-derived class called MyObject, you probably want to define conversion functions for MyObject* that utilize QScriptEngine::newQObject() and QScriptValue::toQObject().)

If you only want to define a common script interface for values of type `T`, and don't care how those values are represented (i.e. storing them in QVariants is fine), use setDefaultPrototype() instead; this will minimize conversion costs.

You need to declare the custom type first with Q_DECLARE_METATYPE().

After a type has been registered, you can convert from a QScriptValue to that type using fromScriptValue(), and create a QScriptValue from a value of that type using toScriptValue(). The engine will take care of calling the proper conversion function when calling C++ slots, and when getting or setting a C++ property; i.e. the custom type may be used seamlessly on both the C++ side and the script side.

The following is an example of how to use this function. We will specify custom conversion of our type `MyStruct`. Here's the C++ type:

      struct MyStruct {
          int x;
          int y;
      };

We must declare it so that the type will be known to QMetaType:

      Q_DECLARE_METATYPE(MyStruct)

Next, the `MyStruct` conversion functions. We represent the `MyStruct` value as a script object and just copy the properties:

      QScriptValue toScriptValue(QScriptEngine *engine, const MyStruct &s)
      {
        QScriptValue obj = engine->newObject();
        obj.setProperty("x", s.x);
        obj.setProperty("y", s.y);
        return obj;
      }

      void fromScriptValue(const QScriptValue &obj, MyStruct &s)
      {
        s.x = obj.property("x").toInt32();
        s.y = obj.property("y").toInt32();
      }

Now we can register `MyStruct` with the engine:

      qScriptRegisterMetaType(engine, toScriptValue, fromScriptValue);

Working with `MyStruct` values is now easy:

      MyStruct s = qscriptvalue_cast<MyStruct>(context->argument(0));
      ...
      MyStruct s2;
      s2.x = s.x + 10;
      s2.y = s.y + 20;
      QScriptValue v = engine->toScriptValue(s2);

If you want to be able to construct values of your custom type from script code, you have to register a constructor function for the type. For example:

      QScriptValue createMyStruct(QScriptContext *, QScriptEngine *engine)
      {
          MyStruct s;
          s.x = 123;
          s.y = 456;
          return engine->toScriptValue(s);
      }
      ...
      QScriptValue ctor = engine.newFunction(createMyStruct);
      engine.globalObject().setProperty("MyStruct", ctor);

See also qScriptRegisterSequenceMetaType() and qRegisterMetaType().

### int qScriptRegisterSequenceMetaType(QScriptEngine *engine, const QScriptValue &prototype = QScriptValue(), T * = 0)

Registers the sequence type `T` in the given engine. This function provides conversion functions that convert between `T` and Qt Script `Array` objects. `T` must provide a const_iterator class and begin(), end() and push_back() functions. If prototype is valid, it will be set as the prototype of `Array` objects due to conversion from `T`; otherwise, the standard `Array` prototype will be used.

Returns the internal ID used by QMetaType.

You need to declare the container type first with Q_DECLARE_METATYPE(). If the element type isn't a standard Qt/C++ type, it must be declared using Q_DECLARE_METATYPE() as well. Example:

      Q_DECLARE_METATYPE(QVector<int>)

      ...

      qScriptRegisterSequenceMetaType<QVector<int> >(engine);
      ...
      QVector<int> v = qscriptvalue_cast<QVector<int> >(engine->evaluate("[5, 1, 3, 2]"));
      std::sort(v.begin(), v.end());
      QScriptValue a = engine->toScriptValue(v);
      qDebug() << a.toString(); // outputs "[1, 2, 3, 5]"

See also qScriptRegisterMetaType().

### QScriptValue qScriptValueFromSequence(QScriptEngine *engine, const Container &container)

Creates an array in the form of a QScriptValue using the given engine with the given container of template type `Container`.

The `Container` type must provide a `const_iterator` class to enable the contents of the container to be copied into the array.

Additionally, the type of each element in the sequence should be suitable for conversion to a QScriptValue. See Conversion Between Qt Script and C++ Types for more information about the restrictions on types that can be used with QScriptValue.

This function was introduced in Qt 4.3.

See also QScriptEngine::fromScriptValue().

### void qScriptValueToSequence(const QScriptValue &value, Container &container)

Copies the elements in the sequence specified by value to the given container of template type `Container`.

The value used is typically an array, but any container can be copied as long as it provides a `length` property describing how many elements it contains.

Additionally, the type of each element in the sequence must be suitable for conversion to a C++ type from a QScriptValue. See Conversion Between Qt Script and C++ Types for more information about the restrictions on types that can be used with QScriptValue.

This function was introduced in Qt 4.3.

See also qscriptvalue_cast().

## Macro Documentation

### Q_SCRIPT_DECLARE_QMETAOBJECT(QMetaObject, ArgType)

Declares the given QMetaObject. Used in combination with QScriptEngine::scriptValueFromQMetaObject() to make enums and instantiation of QMetaObject available to script code. The constructor generated by this macro takes a single argument of type ArgType; typically the argument is the parent type of the new instance, in which case ArgType is `QWidget*` or `QObject*`. Objects created by the constructor will have QScriptEngine::AutoOwnership ownership.

This function was introduced in Qt 4.3.