PySide6.QtQml.QJSValue

class QJSValue

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

Synopsis

Methods

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

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 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.

myEngine = QJSEngine()
myObject = myEngine.newObject()
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());
}

Converting to JSON

It’s possible to convert a QJSValue to a JSON type. For example, to convert to an array, use fromScriptValue() :

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

See also

QJSEngine QJSValueIterator

class SpecialValue

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

Constant

Description

QJSValue.UndefinedValue

An undefined value.

QJSValue.NullValue

A null value.
class 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 URIError 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.
class ObjectConversionBehavior

This enum is used to specify how JavaScript objects and symbols without an equivalent native Qt type should be treated when converting to QVariant.

Constant

Description

QJSValue.ConvertJSObjects

A best-effort, possibly lossy, conversion is attempted. Symbols are converted to QString.

QJSValue.RetainJSObjects

The value is retained as QJSValue wrapped in QVariant.

Added in version 6.1.

__init__([value=QJSValue.SpecialValue.UndefinedValue])
Parameters:

value – SpecialValue

Constructs a new QJSValue with a special value.

__init__(value)
Parameters:

value – bool

Constructs a new QJSValue with a boolean value.

__init__(other)
Parameters:

other – QJSValue

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).

__init__(value)
Parameters:

value – QLatin1String

Constructs a new QJSValue with a string value.

__init__(value)
Parameters:

value – str

Constructs a new QJSValue with a string value.

__init__(str)
Parameters:

str – str

Constructs a new QJSValue with a string value.

__init__(value)
Parameters:

value – float

Constructs a new QJSValue with a number value.

__init__(value)
Parameters:

value – int

Constructs a new QJSValue with a number value.

__init__(value)
Parameters:

value – int

Constructs a new QJSValue with a number value.

call([args=QJSValueList()])
Parameters:

args – .list of QJSValue

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, 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.

callAsConstructor([args=QJSValueList()])
Parameters:

args – .list of QJSValue

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, 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() newObject()

callWithInstance(instance[, args=QJSValueList()])
Parameters:

  • instance – QJSValue

  • args – .list of QJSValue

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()

deleteProperty(name)
Parameters:

name – str

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.

See also

setProperty() hasOwnProperty()

equals(other)
Parameters:

other – QJSValue

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()

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

hasOwnProperty(name)
Parameters:

name – str

Return type:

bool

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

hasProperty(name)
Parameters:

name – str

Return type:

bool

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

isArray()
Return type:

bool

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

See also

newArray()

isBool()
Return type:

bool

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

See also

toBool()

isCallable()
Return type:

bool

Returns true if this QJSValue is a function, otherwise returns false.

See also

call()

isDate()
Return type:

bool

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

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

isNull()
Return type:

bool

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

isNumber()
Return type:

bool

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

See also

toNumber()

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()

isQMetaObject()
Return type:

bool

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

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.

isRegExp()
Return type:

bool

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

isString()
Return type:

bool

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

See also

toString()

isUndefined()
Return type:

bool

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.

isUrl()
Return type:

bool

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

Note

For a QJSValue that contains a QUrl, this function returns false. However, toVariant().value<QUrl>() works in both cases.

isVariant()
Return type:

bool

Note

This function is deprecated.

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

Warning

This function is likely to give unexpected results. A variant value is only constructed by the QJSEngine in a very limited number of cases. This used to be different before Qt 5.14, where toScriptValue would have created them for more types instead of corresponding ECMAScript types. You can get a valid QVariant via toVariant for many values for which isVariant returns false.

See also

toVariant()

property(name)
Parameters:

name – str

Return type:

QJSValue

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.

property(arrayIndex)
Parameters:

arrayIndex – int

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.

prototype()
Return type:

QJSValue

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

setProperty(name, value)
Parameters:

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.

setProperty(arrayIndex, value)
Parameters:

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) Working With Arrays

setPrototype(prototype)
Parameters:

prototype – QJSValue

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.

strictlyEquals(other)
Parameters:

other – QJSValue

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()

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()

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()

toInt()
Return type:

int

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()

toNumber()
Return type:

float

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).

toPrimitive()
Return type:

QJSPrimitiveValue

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 .

Note

Conversion of a managed value to a string can throw an exception. In particular, symbols cannot be coerced into strings, or a custom toString() method may throw. In this case the result is the undefined value and the engine carries an error after the conversion.

toQMetaObject()
Return type:

QMetaObject

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

See also

isQMetaObject()

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 toQObject() to return None even when isQObject() returns true).

See also

isQObject()

toString()
Return type:

str

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()

toUInt()
Return type:

int

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()

toVariant()
Return type:

object

This is an overloaded function.

Returns toVariant ( ConvertJSObjects ).

See also

isVariant()

toVariant(behavior)
Parameters:

behavior – ObjectConversionBehavior

Return type:

object

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:

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() ).

RegularExpression Object

A QVariant containing the regular expression value.

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()