QJSValue Class | Qt QML 5.9

Qt 5.9 | Qt QML | C++ Classes | QJSValue

Qt 5.9.9 Reference Documentation

# QJSValue Class

The QJSValue class acts as a container for Qt/JavaScript data types. More...

Header: | #include <QJSValue>
qmake: | QT += qml
Since: | Qt 5.0

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

## Public Types

enum | SpecialValue { UndefinedValue, NullValue }

## Public Functions

| QJSValue(SpecialValue value = UndefinedValue)
| QJSValue(const QJSValue &other)
| QJSValue(QJSValue &&other)
| QJSValue(bool value)
| QJSValue(int value)
| QJSValue(uint value)
| QJSValue(double value)
| QJSValue(const QString &value)
| QJSValue(const QLatin1String &value)
| QJSValue(const char *value)
| QJSValue(QV4::ExecutionEngine *e, quint64 val)
| ~QJSValue()
QJSValue | call(const QJSValueList &args = QJSValueList())
QJSValue | callAsConstructor(const QJSValueList &args = QJSValueList())
QJSValue | callWithInstance(const QJSValue &instance, const QJSValueList &args = QJSValueList())
bool | deleteProperty(const QString &name)
bool | equals(const QJSValue &other) const
bool | hasOwnProperty(const QString &name) const
bool | hasProperty(const QString &name) const
bool | isArray() const
bool | isBool() const
bool | isCallable() const
bool | isDate() const
bool | isError() const
bool | isNull() const
bool | isNumber() const
bool | isObject() const
bool | isQMetaObject() const
bool | isQObject() const
bool | isRegExp() const
bool | isString() const
bool | isUndefined() const
bool | isVariant() const
QJSValue | property(const QString &name) const
QJSValue | property(quint32 arrayIndex) const
QJSValue | prototype() const
void | setProperty(const QString &name, const QJSValue &value)
void | setProperty(quint32 arrayIndex, const QJSValue &value)
void | setPrototype(const QJSValue &prototype)
bool | strictlyEquals(const QJSValue &other) const
bool | toBool() const
QDateTime | toDateTime() const
qint32 | toInt() const
double | toNumber() const
const QMetaObject * | toQMetaObject() const
QObject * | toQObject() const
QString | toString() const
quint32 | toUInt() const
QVariant | toVariant() const
QJSValue & | operator=(QJSValue &&other)
QJSValue & | operator=(const QJSValue &other)

## Detailed Description

The QJSValue class acts as a container for Qt/JavaScript data types.

QJSValue supports the types defined in the ECMA-262 standard: The primitive types, which are Undefined, Null, Boolean, Number, and String; and the Object and Array types. Additionally, built-in support is provided for Qt/C++ types such as QVariant and QObject.

For the object-based types (including Date and RegExp), use the newT() functions in QJSEngine (e.g. QJSEngine::newObject()) to create a QJSValue of the desired type. For the primitive types, use one of the QJSValue constructor overloads. For other types, e.g. registered gadget types such as QPoint, you can use QJSEngine::toScriptValue.

The methods named isT() (e.g. isBool(), isUndefined()) can be used to test if a value is of a certain type. The methods named toT() (e.g. toBool(), toString()) can be used to convert a QJSValue to another type. You can also use the generic QJSValue_cast() function.

Object values have zero or more properties which are themselves QJSValues. Use setProperty() to set a property of an object, and call property() to retrieve the value of a property.

      QJSEngine myEngine;
      QJSValue myObject = myEngine.newObject();
      QJSValue myOtherObject = myEngine.newObject();
      myObject.setProperty("myChild", myOtherObject);
      myObject.setProperty("name", "John Doe");

If you want to iterate over the properties of a script object, use the QJSValueIterator class.

Object values have an internal `prototype` property, which can be accessed with prototype() and setPrototype().

Function objects (objects for which isCallable()) returns true) can be invoked by calling call(). Constructor functions can be used to construct new objects by calling callAsConstructor().

Use equals() or strictlyEquals() to compare a QJSValue to another.

Note that a QJSValue for which isObject() is true only carries a reference to an actual object; copying the QJSValue will only copy the object reference, not the object itself. If you want to clone an object (i.e. copy an object's properties to another object), you can do so with the help of a `for-in` statement in script code, or QJSValueIterator in C++.

### Working With Arrays

To create an array using QJSValue, use QJSEngine::newArray():

      // Assumes that this class was declared in QML.
      QJSValue jsArray = engine->newArray(3);

To set individual elements in the array, use the setProperty(quint32 arrayIndex, const QJSValue &value) overload. For example, to fill the array above with integers:

      for (int i = 0; i < 3; ++i) {
          jsArray.setProperty(i, QRandomGenerator::global().generate());
      }

To determine the length of the array, access the `"length"` property. To access array elements, use the property(quint32 arrayIndex) overload. The following code reads the array we created above back into a list:

      QVector<int> integers;
      const int length = jsArray.property("length").toInt();
      for (int i = 0; i < length; ++i) {
          integers.append(jsArray.property(i).toInt());
      }

See also QJSEngine and QJSValueIterator.

## Member Type Documentation

### enum QJSValue::SpecialValue

This enum is used to specify a single-valued type.

Constant | Value | Description
--- | --- | ---
`QJSValue::UndefinedValue` | `1` | An undefined value.
`QJSValue::NullValue` | `0` | A null value.

## Member Function Documentation

### QJSValue::QJSValue(SpecialValue value = UndefinedValue)

Constructs a new QJSValue with a special value.

### QJSValue::QJSValue(const QJSValue &other)

Constructs a new QJSValue that is a copy of other.

Note that if other is an object (i.e., isObject() would return true), then only a reference to the underlying object is copied into the new script value (i.e., the object itself is not copied).

### QJSValue::QJSValue(QJSValue &&other)

Move constructor. Moves from other into this QJSValue object.

### QJSValue::QJSValue(bool value)

Constructs a new QJSValue with a boolean value.

### QJSValue::QJSValue(int value)

Constructs a new QJSValue with a number value.

### QJSValue::QJSValue(uint value)

Constructs a new QJSValue with a number value.

### QJSValue::QJSValue(double value)

Constructs a new QJSValue with a number value.

### QJSValue::QJSValue(const QString &value)

Constructs a new QJSValue with a string value.

### QJSValue::QJSValue(const QLatin1String &value)

Constructs a new QJSValue with a string value.

### QJSValue::QJSValue(const char *value)

Constructs a new QJSValue with a string value.

### QJSValue::QJSValue(QV4::ExecutionEngine *e, quint64 val)

Default constructs an instance of QJSValue.

### QJSValue::~QJSValue()

Destroys this QJSValue.

### QJSValue QJSValue::call(const QJSValueList &args = QJSValueList())

Calls this QJSValue as a function, passing args as arguments to the function, and using the globalObject() as the "this"-object. Returns the value returned from the function.

If this QJSValue is not callable, call() does nothing and returns an undefined QJSValue.

Calling call() can cause an exception to occur in the script engine; in that case, call() returns the value that was thrown (typically an `Error` object). You can call isError() on the return value to determine whether an exception occurred.

See also isCallable(), callWithInstance(), and callAsConstructor().

### QJSValue QJSValue::callAsConstructor(const QJSValueList &args = QJSValueList())

Creates a new `Object` and calls this QJSValue as a constructor, using the created object as the `this' object and passing args as arguments. If the return value from the constructor call is an object, then that object is returned; otherwise the default constructed object is returned.

If this QJSValue is not a function, callAsConstructor() does nothing and returns an undefined QJSValue.

Calling this function can cause an exception to occur in the script engine; in that case, the value that was thrown (typically an `Error` object) is returned. You can call isError() on the return value to determine whether an exception occurred.

See also call() and QJSEngine::newObject().

### QJSValue QJSValue::callWithInstance(const QJSValue &instance, const QJSValueList &args = QJSValueList())

Calls this QJSValue as a function, using instance as the `this' object in the function call, and passing args as arguments to the function. Returns the value returned from the function.

If this QJSValue is not a function, call() does nothing and returns an undefined QJSValue.

Note that if instance is not an object, the global object (see QJSEngine::globalObject()) will be used as the `this' object.

Calling call() can cause an exception to occur in the script engine; in that case, call() returns the value that was thrown (typically an `Error` object). You can call isError() on the return value to determine whether an exception occurred.

See also call().

### bool QJSValue::deleteProperty(const QString &name)

Attempts to delete this object's property of the given name. Returns true if the property was deleted, otherwise returns false.

The behavior of this function is consistent with the JavaScript delete operator. In particular:

- Non-configurable properties cannot be deleted.
- This function will return true even if this object doesn't have a property of the given name (i.e., non-existent properties are "trivially deletable").
- If this object doesn't have an own property of the given name, but an object in the prototype() chain does, the prototype object's property is not deleted, and this function returns true.

See also setProperty() and hasOwnProperty().

### bool QJSValue::equals(const QJSValue &other) const

Returns true if this QJSValue is equal to other, otherwise returns false. The comparison follows the behavior described in ECMA-262 section 11.9.3, "The Abstract Equality Comparison Algorithm".

This function can return true even if the type of this QJSValue is different from the type of the other value; i.e. the comparison is not strict. For example, comparing the number 9 to the string "9" returns true; comparing an undefined value to a null value returns true; comparing a `Number` object whose primitive value is 6 to a `String` object whose primitive value is "6" returns true; and comparing the number 1 to the boolean value `true` returns true. If you want to perform a comparison without such implicit value conversion, use strictlyEquals().

Note that if this QJSValue or the other value are objects, calling this function has side effects on the script engine, since the engine will call the object's valueOf() function (and possibly toString()) in an attempt to convert the object to a primitive value (possibly resulting in an uncaught script exception).

See also strictlyEquals().

### bool QJSValue::hasOwnProperty(const QString &name) const

Returns true if this object has an own (not prototype-inherited) property of the given name, otherwise returns false.

See also property() and hasProperty().

### bool QJSValue::hasProperty(const QString &name) const

Returns true if this object has a property of the given name, otherwise returns false.

See also property() and hasOwnProperty().

### bool QJSValue::isArray() const

Returns true if this QJSValue is an object of the Array class; otherwise returns false.

See also QJSEngine::newArray().

### bool QJSValue::isBool() const

Returns true if this QJSValue is of the primitive type Boolean; otherwise returns false.

See also toBool().

### bool QJSValue::isCallable() const

Returns true if this QJSValue can be called a function, otherwise returns false.

See also call().

### bool QJSValue::isDate() const

Returns true if this QJSValue is an object of the Date class; otherwise returns false.

### bool QJSValue::isError() const

Returns true if this QJSValue is an object of the Error class; otherwise returns false.

See also QJSEngine - Script Exceptions.

### bool QJSValue::isNull() const

Returns true if this QJSValue is of the primitive type Null; otherwise returns false.

### bool QJSValue::isNumber() const

Returns true if this QJSValue is of the primitive type Number; otherwise returns false.

See also toNumber().

### bool QJSValue::isObject() const

Returns true if this QJSValue is of the Object type; otherwise returns false.

Note that function values, variant values, and QObject values are objects, so this function returns true for such values.

See also QJSEngine::newObject().

### bool QJSValue::isQMetaObject() const

Returns true if this QJSValue is a QMetaObject; otherwise returns false.

This function was introduced in Qt 5.8.

See also toQMetaObject() and QJSEngine::newQMetaObject().

### bool QJSValue::isQObject() const

Returns true if this QJSValue is a QObject; otherwise returns false.

Note: This function returns true even if the QObject that this QJSValue wraps has been deleted.

See also toQObject() and QJSEngine::newQObject().

### bool QJSValue::isRegExp() const

Returns true if this QJSValue is an object of the RegExp class; otherwise returns false.

### bool QJSValue::isString() const

Returns true if this QJSValue is of the primitive type String; otherwise returns false.

See also toString().

### bool QJSValue::isUndefined() const

Returns true if this QJSValue is of the primitive type Undefined; otherwise returns false.

### bool QJSValue::isVariant() const

Returns true if this QJSValue is a variant value; otherwise returns false.

See also toVariant().

### QJSValue QJSValue::property(const QString &name) const

Returns the value of this QJSValue's property with the given name. 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 script engine, since the getter function will be called (possibly resulting in an uncaught script exception). If an exception occurred, property() returns the value that was thrown (typically an `Error` object).

To access array elements, use the setProperty(quint32 arrayIndex, const QJSValue &value) overload instead.

See also setProperty(), hasProperty(), and QJSValueIterator.

### QJSValue QJSValue::property(quint32 arrayIndex) const

This is an overloaded function.

Returns the property at the given arrayIndex.

It is possible to access elements in an array in two ways. The first is to use the array index as the property name:

      qDebug() << jsValueArray.property(QLatin1String("4")).toString();

The second is to use the overload that takes an index:

      qDebug() << jsValueArray.property(4).toString();

Both of these approaches achieve the same result, except that the latter:

- Is easier to use (can use an integer directly)
- Is faster (no conversion to integer)

If this QJSValue is not an Array object, this function behaves as if property() was called with the string representation of arrayIndex.

### QJSValue QJSValue::prototype() const

If this QJSValue is an object, returns the internal prototype (`__proto__` property) of this object; otherwise returns an undefined QJSValue.

See also setPrototype() and isObject().

### void QJSValue::setProperty(const QString &name, const QJSValue &value)

Sets the value of this QJSValue's property with the given name to the given value.

If this QJSValue is not an object, this function does nothing.

If this QJSValue does not already have a property with name name, a new property is created.

To modify array elements, use the setProperty(quint32 arrayIndex, const QJSValue &value) overload instead.

See also property() and deleteProperty().

### void QJSValue::setProperty(quint32 arrayIndex, const QJSValue &value)

This is an overloaded function.

Sets the property at the given arrayIndex to the given value.

It is possible to modify elements in an array in two ways. The first is to use the array index as the property name:

      jsValueArray.setProperty(QLatin1String("4"), value);

The second is to use the overload that takes an index:

      jsValueArray.setProperty(4, value);

Both of these approaches achieve the same result, except that the latter:

- Is easier to use (can use an integer directly)
- Is faster (no conversion to integer)

If this QJSValue is not an Array object, this function behaves as if setProperty() was called with the string representation of arrayIndex.

See also property(quint32 arrayIndex) and Working With Arrays.

### void QJSValue::setPrototype(const QJSValue &prototype)

If this QJSValue is an object, sets the internal prototype (`__proto__` property) of this object to be prototype; if the QJSValue is null, it sets the prototype to null; otherwise does nothing.

The internal prototype should not be confused with the public property with name "prototype"; the public prototype is usually only set on functions that act as constructors.

See also prototype() and isObject().

### bool QJSValue::strictlyEquals(const QJSValue &other) const

Returns true if this QJSValue is equal to other using strict comparison (no conversion), otherwise returns false. The comparison follows the behavior described in ECMA-262 section 11.9.6, "The Strict Equality Comparison Algorithm".

If the type of this QJSValue is different from the type of the other value, this function returns false. If the types are equal, the result depends on the type, as shown in the following table:

Type | Result
--- | ---
Undefined | true
Null | true
Boolean | true if both values are true, false otherwise
Number | false if either value is NaN (Not-a-Number); true if values are equal, false otherwise
String | true if both values are exactly the same sequence of characters, false otherwise
Object | true if both values refer to the same object, false otherwise

See also equals().

### bool QJSValue::toBool() const

Returns the boolean value of this QJSValue, using the conversion rules described in ECMA-262 section 9.2, "ToBoolean".

Note that if this QJSValue is an object, calling this function has side effects on the script engine, since the engine will call the object's valueOf() function (and possibly toString()) in an attempt to convert the object to a primitive value (possibly resulting in an uncaught script exception).

See also isBool().

### QDateTime QJSValue::toDateTime() const

Returns a QDateTime representation of this value, in local time. If this QJSValue is not a date, or the value of the date is NaN (Not-a-Number), an invalid QDateTime is returned.

See also isDate().

### qint32 QJSValue::toInt() const

Returns the signed 32-bit integer value of this QJSValue, using the conversion rules described in ECMA-262 section 9.5, "ToInt32".

Note that if this QJSValue is an object, calling this function has side effects on the script engine, since the engine will call the object's valueOf() function (and possibly toString()) in an attempt to convert the object to a primitive value (possibly resulting in an uncaught script exception).

See also toNumber() and toUInt().

### double QJSValue::toNumber() const

Returns the number value of this QJSValue, as defined in ECMA-262 section 9.3, "ToNumber".

Note that if this QJSValue is an object, calling this function has side effects on the script engine, since the engine will call the object's valueOf() function (and possibly toString()) in an attempt to convert the object to a primitive value (possibly resulting in an uncaught script exception).

See also isNumber(), toInt(), and toUInt().

### const QMetaObject *QJSValue::toQMetaObject() const

* If this QJSValue is a QMetaObject, returns the QMetaObject pointer * that the QJSValue represents; otherwise, returns 0. * *

This function was introduced in Qt 5.8.

See also isQMetaObject().

### QObject *QJSValue::toQObject() const

If this QJSValue is a QObject, returns the QObject pointer that the QJSValue represents; otherwise, returns 0.

If the QObject that this QJSValue wraps has been deleted, this function returns 0 (i.e. it is possible for toQObject() to return 0 even when isQObject() returns true).

See also isQObject().

### QString QJSValue::toString() const

Returns the string value of this QJSValue, as defined in ECMA-262 section 9.8, "ToString".

Note that if this QJSValue is an object, calling this function has side effects on the script engine, since the engine will call the object's toString() function (and possibly valueOf()) in an attempt to convert the object to a primitive value (possibly resulting in an uncaught script exception).

See also isString().

### quint32 QJSValue::toUInt() const

Returns the unsigned 32-bit integer value of this QJSValue, using the conversion rules described in ECMA-262 section 9.6, "ToUint32".

Note that if this QJSValue is an object, calling this function has side effects on the script engine, since the engine will call the object's valueOf() function (and possibly toString()) in an attempt to convert the object to a primitive value (possibly resulting in an uncaught script exception).

See also toNumber() and toInt().

### QVariant QJSValue::toVariant() const

Returns the QVariant value of this QJSValue, if it can be converted to a QVariant; otherwise returns an invalid QVariant. The conversion is performed according to the following table:

Input Type | Result
--- | ---
Undefined | An invalid QVariant.
Null | A QVariant containing a null pointer (QMetaType::Nullptr).
Boolean | A QVariant containing the value of the boolean.
Number | A QVariant containing the value of the number.
String | A QVariant containing the value of the string.
QVariant Object | The result is the QVariant value of the object (no conversion).
QObject Object | A QVariant containing a pointer to the QObject.
Date Object | A QVariant containing the date value (toDateTime()).
RegExp Object | A QVariant containing the regular expression value.
Array Object | The array is converted to a QVariantList. Each element is converted to a QVariant, recursively; cyclic references are not followed.
Object | The object is converted to a QVariantMap. Each property is converted to a QVariant, recursively; cyclic references are not followed.

See also isVariant().

### QJSValue &QJSValue::operator=(QJSValue &&other)

Move-assigns other to this QJSValue object.

### QJSValue &QJSValue::operator=(const QJSValue &other)

Assigns the other value to this QJSValue.

Note that if other is an object (isObject() returns true), only a reference to the underlying object will be assigned; the object itself will not be copied.