QJSValue

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

Inheritance diagram of PySide2.QtQml.QJSValue

Synopsis

Functions

Detailed Description

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. 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 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 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 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());
}
class QJSValue([value=UndefinedValue])

QJSValue(value)

QJSValue(other)

QJSValue(value)

QJSValue(str)

QJSValue(value)

QJSValue(value)

QJSValue(value)

param str

str

param other

QJSValue

param value

SpecialValue

Constructs a new QJSValue with a special value .

Constructs a new QJSValue with a boolean value .

Constructs a new QJSValue with a string value .

Constructs a new QJSValue with a number value .

Constructs a new QJSValue with a number value .

Constructs a new QJSValue with a number value .

PySide2.QtQml.QJSValue.SpecialValue

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

Constant

Description

QJSValue.UndefinedValue

An undefined value.

QJSValue.NullValue

A null value.

PySide2.QtQml.QJSValue.ErrorType

Use this enum for JavaScript language-specific types of Error objects.

They may be useful when emulating language features in C++ requires the use of specialized exception types. In addition, they may help to more clearly communicate certain typical conditions, instead of throwing a generic JavaScript exception. For example, code that deals with networking and resource locators may find it useful to propagate errors related to malformed locators using the type.

Constant

Description

QJSValue.GenericError

A generic Error object, but not of a specific sub-type.

QJSValue.RangeError

A value did not match the expected set or range.

QJSValue.ReferenceError

A non-existing variable referenced.

QJSValue.SyntaxError

An invalid token or sequence of tokens was encountered that does not conform with the syntax of the language.

QJSValue.TypeError

An operand or argument is incompatible with the type expected.

QJSValue.URIError

A URI handling function was used incorrectly or the URI provided is malformed.

New in version 5.12.

PySide2.QtQml.QJSValue.call([args=QJSValueList()])
Parameters

args

Return type

QJSValue

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, does nothing and returns an undefined QJSValue .

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

PySide2.QtQml.QJSValue.callAsConstructor([args=QJSValueList()])
Parameters

args

Return type

QJSValue

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, 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() newObject()

PySide2.QtQml.QJSValue.callWithInstance(instance[, args=QJSValueList()])
Parameters
Return type

QJSValue

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 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()

PySide2.QtQml.QJSValue.deleteProperty(name)
Parameters

name – unicode

Return type

bool

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.

PySide2.QtQml.QJSValue.engine()
Return type

QJSEngine

Note

This function is deprecated.

Returns the QJSEngine that created this QJSValue , or 0 if this QJSValue is invalid or the value is not associated with a particular engine.

PySide2.QtQml.QJSValue.equals(other)
Parameters

otherQJSValue

Return type

bool

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()

PySide2.QtQml.QJSValue.errorType()
Return type

ErrorType

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

See also

isError() QJSEngine - Script Exceptions

PySide2.QtQml.QJSValue.hasOwnProperty(name)
Parameters

name – unicode

Return type

bool

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

PySide2.QtQml.QJSValue.hasProperty(name)
Parameters

name – unicode

Return type

bool

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

PySide2.QtQml.QJSValue.isArray()
Return type

bool

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

See also

newArray()

PySide2.QtQml.QJSValue.isBool()
Return type

bool

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

See also

toBool()

PySide2.QtQml.QJSValue.isCallable()
Return type

bool

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

See also

call()

PySide2.QtQml.QJSValue.isDate()
Return type

bool

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

PySide2.QtQml.QJSValue.isError()
Return type

bool

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

See also

errorType() QJSEngine - Script Exceptions

PySide2.QtQml.QJSValue.isNull()
Return type

bool

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

PySide2.QtQml.QJSValue.isNumber()
Return type

bool

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

See also

toNumber()

PySide2.QtQml.QJSValue.isObject()
Return type

bool

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

newObject()

PySide2.QtQml.QJSValue.isQMetaObject()
Return type

bool

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

PySide2.QtQml.QJSValue.isQObject()
Return type

bool

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.

PySide2.QtQml.QJSValue.isRegExp()
Return type

bool

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

PySide2.QtQml.QJSValue.isString()
Return type

bool

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

See also

toString()

PySide2.QtQml.QJSValue.isUndefined()
Return type

bool

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

PySide2.QtQml.QJSValue.isVariant()
Return type

bool

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

See also

toVariant()

PySide2.QtQml.QJSValue.property(name)
Parameters

name – unicode

Return type

QJSValue

PySide2.QtQml.QJSValue.property(arrayIndex)
Parameters

arrayIndexquint32

Return type

QJSValue

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 .

PySide2.QtQml.QJSValue.prototype()
Return type

QJSValue

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

PySide2.QtQml.QJSValue.setProperty(arrayIndex, value)
Parameters
  • arrayIndexquint32

  • valueQJSValue

PySide2.QtQml.QJSValue.setProperty(name, value)
Parameters
PySide2.QtQml.QJSValue.setPrototype(prototype)
Parameters

prototypeQJSValue

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.

PySide2.QtQml.QJSValue.strictlyEquals(other)
Parameters

otherQJSValue

Return type

bool

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()

PySide2.QtQml.QJSValue.toBool()
Return type

bool

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()

PySide2.QtQml.QJSValue.toDateTime()
Return type

QDateTime

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()

PySide2.QtQml.QJSValue.toInt()
Return type

qint32

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() toUInt()

PySide2.QtQml.QJSValue.toNumber()
Return type

double

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).

PySide2.QtQml.QJSValue.toQMetaObject()
Return type

QMetaObject

* If this QJSValue is a QMetaObject , returns the QMetaObject pointer * that the QJSValue represents; otherwise, returns None . * *

See also

isQMetaObject()

PySide2.QtQml.QJSValue.toQObject()
Return type

QObject

If this QJSValue is a QObject , returns the QObject pointer that the QJSValue represents; otherwise, returns None .

If the QObject that this QJSValue wraps has been deleted, this function returns None (i.e. it is possible for to return None even when isQObject() returns true).

See also

isQObject()

PySide2.QtQml.QJSValue.toString()
Return type

unicode

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 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()

PySide2.QtQml.QJSValue.toUInt()
Return type

quint32

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() toInt()

PySide2.QtQml.QJSValue.toVariant()
Return type

object

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 ( 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()