QJSValue Class

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

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

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

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

const QJsonValue jsonValue = engine.fromScriptValue<QJsonValue>(jsValue);
const QJsonArray jsonArray = jsonValue.toArray();

Member Function Documentation

QJSValue::QJSValue(const char *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 QString &value)

Constructs a new QJSValue with a string value.

QJSValue::QJSValue(double value)

Constructs a new QJSValue with a number value.

QJSValue::QJSValue(uint value)

Constructs a new QJSValue with a number value.

QJSValue::QJSValue(int value)

Constructs a new QJSValue with a number value.

QJSValue::QJSValue(bool value)

Constructs a new QJSValue with a boolean value.

QJSValue::QJSValue(QJSValue &&other)

Move constructor. Moves from other into this QJSValue object.

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::SpecialValue value = UndefinedValue)

Constructs a new QJSValue with a special value.

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.

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

Move-assigns other to this QJSValue object.

QJSValue::~QJSValue()

Destroys this QJSValue.

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

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()) const

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()) const

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().

[since 5.12] QJSValue::ErrorType QJSValue::errorType() const

Returns the error type this QJSValue represents if it is an Error object. Otherwise, returns NoError."

This function was introduced in Qt 5.12.

See also isError() and QJSEngine - Script Exceptions.

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 is 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 errorType() and 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().

[since 5.8] 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 or if the managed value has been cleared (by deleting the engine). Otherwise returns false.

bool QJSValue::isUrl() const

Returns true if this QJSValue is an object of the URL class; 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:

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().

QJSPrimitiveValue QJSValue::toPrimitive() const

Converts the value to a QJSPrimitiveValue. If the value holds a type supported by QJSPrimitiveValue, the value is copied. Otherwise the value is converted to a string, and the string is stored in QJSPrimitiveValue.

[since 5.8] const QMetaObject *QJSValue::toQMetaObject() const

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

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 nullptr.

If the QObject that this QJSValue wraps has been deleted, this function returns nullptr (i.e. it is possible for toQObject() to return nullptr 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(QJSValue::ObjectConversionBehavior behavior) const

Returns the QVariant value of this QJSValue, if it can be converted to a QVariant; otherwise returns an invalid QVariant. Some JavaScript types and objects have native expressions in Qt. Those are converted to their native expressions. For example:

For other types the behavior parameter is relevant. If ConvertJSObjects is given, a best effort but possibly lossy conversion is attempted. Generic JavaScript objects are converted to QVariantMap. JavaScript arrays are converted to QVariantList. Each property or element is converted to a QVariant, recursively; cyclic references are not followed. JavaScript function objects are dropped. If RetainJSObjects is given, the QJSValue is wrapped into a QVariant via QVariant::fromValue(). The resulting conversion is lossless but the internal structure of the objects is not immediately accessible.

See also isVariant().

QVariant QJSValue::toVariant() const

This is an overloaded function.

Returns toVariant(ConvertJSObjects).

See also isVariant().