JsObject

class JsObject

A proxy on a JavaScript object.

The properties of the JavaScript object are accessible via the [] and []= operators. Methods are callable via callMethod.

Implementers

• JsArray<E>
• JsFunction

Constructors

JsObject() factory

factory JsObject(JsFunction constructor, [List<dynamic>? arguments])

Constructs a JavaScript object from its native constructor and returns a proxy to it.

Implementation

external factory JsObject(JsFunction constructor, [List? arguments]);

JsObject.fromBrowserObject() factory

factory JsObject.fromBrowserObject(Object object)

Constructs a JsObject that proxies a native Dart object; for expert use only.

Use this constructor only if you wish to get access to JavaScript properties attached to a browser host object, such as a Node or Blob, that is normally automatically converted into a native Dart object.

An exception will be thrown if object has the type bool, num, or String.

Implementation

external factory JsObject.fromBrowserObject(Object object);

JsObject.jsify() factory

factory JsObject.jsify(Object object)

Recursively converts a JSON-like collection of Dart objects to a collection of JavaScript objects and returns a JsObject proxy to it.

object must be a Map or Iterable, the contents of which are also converted. Maps and Iterables are copied to a new JavaScript object. Primitives and other transferable values are directly converted to their JavaScript type, and all other objects are proxied.

Implementation

external factory JsObject.jsify(Object object);

Properties

hashCode no setter override

int get hashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Implementation

int get hashCode => 0;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

Methods

callMethod()

dynamic callMethod(Object method, [List<dynamic>? args])

Calls method on the JavaScript object with the arguments args and returns the result.

The type of method must be either String or num.

Implementation

external dynamic callMethod(Object method, [List? args]);

deleteProperty()

void deleteProperty(Object property)

Removes property from the JavaScript object.

This is the equivalent of the delete operator in JavaScript.

Implementation

external void deleteProperty(Object property);

hasProperty()

bool hasProperty(Object property)

Returns true if the JavaScript object contains the specified property either directly or though its prototype chain.

This is the equivalent of the in operator in JavaScript.

Implementation

external bool hasProperty(Object property);

instanceof()

bool instanceof(JsFunction type)

Returns true if the JavaScript object has type in its prototype chain.

This is the equivalent of the instanceof operator in JavaScript.

Implementation

external bool instanceof(JsFunction type);

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

toString() override

String toString()

Returns the result of the JavaScript objects toString method.

Implementation

external String toString();

Operators

operator ==() override

bool operator ==(Object other)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Implementation

external bool operator ==(Object other);

operator

dynamic operator [](Object property)

Returns the value associated with property from the proxied JavaScript object.

The type of property must be either String or num.

Implementation

external dynamic operator [](Object property);

operator []=()

void operator []=(Object property, Object? value)

Implementation

external void operator []=(Object property, Object? value);