Observable (utils)

@ckeditor/ckeditor5-utils/src/observablemixin

class MyClass extends ObservableMixin( OtherBaseClass ) {
	// This class now implements the `Observable` interface.
}

Methods

• bind( bindProperties ) → MultiBindChainmodule:utils/observablemixin~Observable#bind:MANY_BIND

  See source

  Binds observable properties to other objects implementing the Observable interface.

  Read more in the dedicated guide covering the topic of property bindings with some additional examples.

  Consider two objects: a button and an associated command (both Observable).

  A simple property binding could be as follows:

  button.bind( 'isEnabled' ).to( command, 'isEnabled' );
  

  or even shorter:

  button.bind( 'isEnabled' ).to( command );
  

  which works in the following way:

  • button.isEnabled instantly equals command.isEnabled,
  • whenever command.isEnabled changes, button.isEnabled will immediately reflect its value.

  Note: To release the binding, use unbind.

  You can also "rename" the property in the binding by specifying the new name in the to() chain:

  button.bind( 'isEnabled' ).to( command, 'isWorking' );
  

  It is possible to bind more than one property at a time to shorten the code:

  button.bind( 'isEnabled', 'value' ).to( command );
  

  which corresponds to:

  button.bind( 'isEnabled' ).to( command );
  button.bind( 'value' ).to( command );
  

  The binding can include more than one observable, combining multiple data sources in a custom callback:

  button.bind( 'isEnabled' ).to( command, 'isEnabled', ui, 'isVisible',
  	( isCommandEnabled, isUIVisible ) => isCommandEnabled && isUIVisible );
  

  Using a custom callback allows processing the value before passing it to the target property:

  button.bind( 'isEnabled' ).to( command, 'value', value => value === 'heading1' );
  

  It is also possible to bind to the same property in an array of observables. To bind a button to multiple commands (also Observables) so that each and every one of them must be enabled for the button to become enabled, use the following code:

  button.bind( 'isEnabled' ).toMany( [ commandA, commandB, commandC ], 'isEnabled',
  	( isAEnabled, isBEnabled, isCEnabled ) => isAEnabled && isBEnabled && isCEnabled );
  

  Parameters

  bindProperties : Array<'off' | 'on' | 'once' | 'listenTo' | 'stopListening' | 'fire' | 'delegate' | 'stopDelegating' | 'set' | 'bind' | 'unbind' | 'decorate'>

  Observable properties that will be bound to other observable(s).

  Returns

  MultiBindChain

  The bind chain with the to() and toMany() methods.

• bind( bindProperty1, bindProperty2 ) → DualBindChain<K1, Observable[ K1 ], K2, Observable[ K2 ]>module:utils/observablemixin~Observable#bind:DUAL_BIND

  See source

  Binds observable properties to other objects implementing the Observable interface.

  Read more in the dedicated guide covering the topic of property bindings with some additional examples.

  Consider two objects: a button and an associated command (both Observable).

  A simple property binding could be as follows:

  button.bind( 'isEnabled' ).to( command, 'isEnabled' );
  

  or even shorter:

  button.bind( 'isEnabled' ).to( command );
  

  which works in the following way:

  • button.isEnabled instantly equals command.isEnabled,
  • whenever command.isEnabled changes, button.isEnabled will immediately reflect its value.

  Note: To release the binding, use unbind.

  You can also "rename" the property in the binding by specifying the new name in the to() chain:

  button.bind( 'isEnabled' ).to( command, 'isWorking' );
  

  It is possible to bind more than one property at a time to shorten the code:

  button.bind( 'isEnabled', 'value' ).to( command );
  

  which corresponds to:

  button.bind( 'isEnabled' ).to( command );
  button.bind( 'value' ).to( command );
  

  The binding can include more than one observable, combining multiple data sources in a custom callback:

  button.bind( 'isEnabled' ).to( command, 'isEnabled', ui, 'isVisible',
  	( isCommandEnabled, isUIVisible ) => isCommandEnabled && isUIVisible );
  

  Using a custom callback allows processing the value before passing it to the target property:

  button.bind( 'isEnabled' ).to( command, 'value', value => value === 'heading1' );
  

  It is also possible to bind to the same property in an array of observables. To bind a button to multiple commands (also Observables) so that each and every one of them must be enabled for the button to become enabled, use the following code:

  button.bind( 'isEnabled' ).toMany( [ commandA, commandB, commandC ], 'isEnabled',
  	( isAEnabled, isBEnabled, isCEnabled ) => isAEnabled && isBEnabled && isCEnabled );
  

  Type parameters

  K1

  K2

  Parameters

  bindProperty1 : K1

  Observable property that will be bound to other observable(s).

  bindProperty2 : K2

  Observable property that will be bound to other observable(s).

  Returns

  DualBindChain<K1, Observable[ K1 ], K2, Observable[ K2 ]>

  The bind chain with the to() and toMany() methods.

• bind( bindProperty ) → SingleBindChain<K, Observable[ K ]>module:utils/observablemixin~Observable#bind:SINGLE_BIND

  See source

  Binds observable properties to other objects implementing the Observable interface.

  Read more in the dedicated guide covering the topic of property bindings with some additional examples.

  Consider two objects: a button and an associated command (both Observable).

  A simple property binding could be as follows:

  button.bind( 'isEnabled' ).to( command, 'isEnabled' );
  

  or even shorter:

  button.bind( 'isEnabled' ).to( command );
  

  which works in the following way:

  • button.isEnabled instantly equals command.isEnabled,
  • whenever command.isEnabled changes, button.isEnabled will immediately reflect its value.

  Note: To release the binding, use unbind.

  You can also "rename" the property in the binding by specifying the new name in the to() chain:

  button.bind( 'isEnabled' ).to( command, 'isWorking' );
  

  It is possible to bind more than one property at a time to shorten the code:

  button.bind( 'isEnabled', 'value' ).to( command );
  

  which corresponds to:

  button.bind( 'isEnabled' ).to( command );
  button.bind( 'value' ).to( command );
  

  The binding can include more than one observable, combining multiple data sources in a custom callback:

  button.bind( 'isEnabled' ).to( command, 'isEnabled', ui, 'isVisible',
  	( isCommandEnabled, isUIVisible ) => isCommandEnabled && isUIVisible );
  

  Using a custom callback allows processing the value before passing it to the target property:

  button.bind( 'isEnabled' ).to( command, 'value', value => value === 'heading1' );
  

  It is also possible to bind to the same property in an array of observables. To bind a button to multiple commands (also Observables) so that each and every one of them must be enabled for the button to become enabled, use the following code:

  button.bind( 'isEnabled' ).toMany( [ commandA, commandB, commandC ], 'isEnabled',
  	( isAEnabled, isBEnabled, isCEnabled ) => isAEnabled && isBEnabled && isCEnabled );
  

  Type parameters

  K

  Parameters

  bindProperty : K

  Observable property that will be bound to other observable(s).

  Returns

  SingleBindChain<K, Observable[ K ]>

  The bind chain with the to() and toMany() methods.

• decorate( methodName ) → voidmodule:utils/observablemixin~Observable#decorate

  See source

  Turns the given methods of this object into event-based ones. This means that the new method will fire an event (named after the method) and the original action will be plugged as a listener to that event.

  Read more in the dedicated guide covering the topic of decorating methods with some additional examples.

  Decorating the method does not change its behavior (it only adds an event), but it allows to modify it later on by listening to the method's event.

  For example, to cancel the method execution the event can be stopped:

  class Foo extends ObservableMixin() {
  	constructor() {
  		super();
  		this.decorate( 'method' );
  	}
  
  	method() {
  		console.log( 'called!' );
  	}
  }
  
  const foo = new Foo();
  foo.on( 'method', ( evt ) => {
  	evt.stop();
  }, { priority: 'high' } );
  
  foo.method(); // Nothing is logged.
  

  Note: The high priority listener has been used to execute this particular callback before the one which calls the original method (which uses the "normal" priority).

  It is also possible to change the returned value:

  foo.on( 'method', ( evt ) => {
  	evt.return = 'Foo!';
  } );
  
  foo.method(); // -> 'Foo'
  

  Finally, it is possible to access and modify the arguments the method is called with:

  method( a, b ) {
  	console.log( `${ a }, ${ b }`  );
  }
  
  // ...
  
  foo.on( 'method', ( evt, args ) => {
  	args[ 0 ] = 3;
  
  	console.log( args[ 1 ] ); // -> 2
  }, { priority: 'high' } );
  
  foo.method( 1, 2 ); // -> '3, 2'
  

  Parameters

  methodName : 'off' | 'on' | 'once' | 'listenTo' | 'stopListening' | 'fire' | 'delegate' | 'stopDelegating' | 'set' | 'bind' | 'unbind' | 'decorate'

  Name of the method to decorate.

  Returns

  void

• inherited

  delegate( events ) → EmitterMixinDelegateChainmodule:utils/observablemixin~Observable#delegate

  See source

  Delegates selected events to another Emitter. For instance:

  emitterA.delegate( 'eventX' ).to( emitterB );
  emitterA.delegate( 'eventX', 'eventY' ).to( emitterC );
  

  then eventX is delegated (fired by) emitterB and emitterC along with data:

  emitterA.fire( 'eventX', data );
  

  and eventY is delegated (fired by) emitterC along with data:

  emitterA.fire( 'eventY', data );
  

  Parameters

  events : Array<string>

  Event names that will be delegated to another emitter.

  Returns

  EmitterMixinDelegateChain

• inherited

  fire( eventOrInfo, args ) → GetEventInfo<TEvent>[ 'return' ]module:utils/observablemixin~Observable#fire

  See source

  Fires an event, executing all callbacks registered for it.

  The first parameter passed to callbacks is an EventInfo object, followed by the optional args provided in the fire() method call.

  Type parameters

  TEvent : extends BaseEvent

  The type describing the event. See BaseEvent.

  Parameters

  eventOrInfo : GetNameOrEventInfo<TEvent>

  The name of the event or EventInfo object if event is delegated.

  args : TEvent[ 'args' ]

  Additional arguments to be passed to the callbacks.

  Returns

  GetEventInfo<TEvent>[ 'return' ]

  By default the method returns undefined. However, the return value can be changed by listeners through modification of the evt.return's property (the event info is the first param of every callback).

• inherited

  listenTo( emitter, event, callback, [ options ] ) → voidmodule:utils/observablemixin~Observable#listenTo:BASE_EMITTER

  See source

  Registers a callback function to be executed when an event is fired in a specific (emitter) object.

  Events can be grouped in namespaces using :. When namespaced event is fired, it additionally fires all callbacks for that namespace.

  // myEmitter.on( ... ) is a shorthand for myEmitter.listenTo( myEmitter, ... ).
  myEmitter.on( 'myGroup', genericCallback );
  myEmitter.on( 'myGroup:myEvent', specificCallback );
  
  // genericCallback is fired.
  myEmitter.fire( 'myGroup' );
  // both genericCallback and specificCallback are fired.
  myEmitter.fire( 'myGroup:myEvent' );
  // genericCallback is fired even though there are no callbacks for "foo".
  myEmitter.fire( 'myGroup:foo' );
  

  An event callback can stop the event and set the return value of the fire method.

  Type parameters

  TEvent : extends BaseEvent

  The type describing the event. See BaseEvent.

  Parameters

  emitter : Emitter

  The object that fires the event.

  event : TEvent[ 'name' ]

  The name of the event.

  callback : GetCallback<TEvent>

  The function to be called on event.

  [ options ] : GetCallbackOptions<TEvent>

  Additional options.

  Returns

  void

• inherited

  off( event, callback ) → voidmodule:utils/observablemixin~Observable#off

  See source

  Stops executing the callback on the given event. Shorthand for this.stopListening( this, event, callback ).

  Parameters

  event : string

  The name of the event.

  callback : Function

  The function to stop being called.

  Returns

  void

• inherited

  on( event, callback, [ options ] ) → voidmodule:utils/observablemixin~Observable#on

  See source

  Registers a callback function to be executed when an event is fired.

  Shorthand for this.listenTo( this, event, callback, options ) (it makes the emitter listen on itself).

  Type parameters

  TEvent : extends BaseEvent

  The type descibing the event. See BaseEvent.

  Parameters

  event : TEvent[ 'name' ]

  The name of the event.

  callback : GetCallback<TEvent>

  The function to be called on event.

  [ options ] : GetCallbackOptions<TEvent>

  Additional options.

  Returns

  void

• inherited

  once( event, callback, [ options ] ) → voidmodule:utils/observablemixin~Observable#once

  See source

  Registers a callback function to be executed on the next time the event is fired only. This is similar to calling on followed by off in the callback.

  Type parameters

  TEvent : extends BaseEvent

  The type descibing the event. See BaseEvent.

  Parameters

  event : TEvent[ 'name' ]

  The name of the event.

  callback : GetCallback<TEvent>

  The function to be called on event.

  [ options ] : GetCallbackOptions<TEvent>

  Additional options.

  Returns

  void

• set( values ) → voidmodule:utils/observablemixin~Observable#set:OBJECT

  See source

  Creates and sets the value of an observable properties of this object. Such a property becomes a part of the state and is observable.

  It accepts a single object literal containing key/value pairs with properties to be set.

  This method throws the observable-set-cannot-override error if the observable instance already has a property with the given property name. This prevents from mistakenly overriding existing properties and methods, but means that foo.set( 'bar', 1 ) may be slightly slower than foo.bar = 1.

  In TypeScript, those properties should be declared in class using declare keyword. In example:

  public declare myProp1: number;
  public declare myProp2: string;
  
  constructor() {
  	this.set( {
  		'myProp1: 2,
  		'myProp2: 'foo'
  	} );
  }
  

  Parameters

  values : object

  An object with name=>value pairs.

  Returns

  void

• set( name, value ) → voidmodule:utils/observablemixin~Observable#set:KEY_VALUE

  See source

  Creates and sets the value of an observable property of this object. Such a property becomes a part of the state and is observable.

  This method throws the observable-set-cannot-override error if the observable instance already has a property with the given property name. This prevents from mistakenly overriding existing properties and methods, but means that foo.set( 'bar', 1 ) may be slightly slower than foo.bar = 1.

  In TypeScript, those properties should be declared in class using declare keyword. In example:

  public declare myProp: number;
  
  constructor() {
  	this.set( 'myProp', 2 );
  }
  

  Type parameters

  K

  Parameters

  name : K

  The property's name.

  value : Observable[ K ]

  The property's value.

  Returns

  void

• inherited

  stopDelegating( [ event ], [ emitter ] ) → voidmodule:utils/observablemixin~Observable#stopDelegating

  See source

  Stops delegating events. It can be used at different levels:

  • To stop delegating all events.
  • To stop delegating a specific event to all emitters.
  • To stop delegating a specific event to a specific emitter.

  Parameters

  [ event ] : string

  The name of the event to stop delegating. If omitted, stops it all delegations.

  [ emitter ] : Emitter

  (requires event) The object to stop delegating a particular event to. If omitted, stops delegation of event to all emitters.

  Returns

  void

• inherited

  stopListening( [ emitter ], [ event ], [ callback ] ) → voidmodule:utils/observablemixin~Observable#stopListening:BASE_STOP

  See source

  Stops listening for events. It can be used at different levels:

  • To stop listening to a specific callback.
  • To stop listening to a specific event.
  • To stop listening to all events fired by a specific object.
  • To stop listening to all events fired by all objects.

  Parameters

  [ emitter ] : Emitter

  The object to stop listening to. If omitted, stops it for all objects.

  [ event ] : string

  (Requires the emitter) The name of the event to stop listening to. If omitted, stops it for all events from emitter.

  [ callback ] : Function

  (Requires the event) The function to be removed from the call list for the given event.

  Returns

  void

• unbind( unbindProperties ) → voidmodule:utils/observablemixin~Observable#unbind

  See source

  Removes the binding created with bind.

  // Removes the binding for the 'a' property.
  A.unbind( 'a' );
  
  // Removes bindings for all properties.
  A.unbind();
  

  Parameters

  unbindProperties : Array<'off' | 'on' | 'once' | 'listenTo' | 'stopListening' | 'fire' | 'delegate' | 'stopDelegating' | 'set' | 'bind' | 'unbind' | 'decorate'>

  Observable properties to be unbound. All the bindings will be released if no properties are provided.

  Returns

  void

Events

• change:{property}( eventInfo, name, value, oldValue )module:utils/observablemixin~Observable#event:change:{property}

  See source

  Fired when a property changed value.

  observable.set( 'prop', 1 );
  
  observable.on<ObservableChangeEvent<number>>( 'change:prop', ( evt, propertyName, newValue, oldValue ) => {
  	console.log( `${ propertyName } has changed from ${ oldValue } to ${ newValue }` );
  } );
  
  observable.prop = 2; // -> 'prop has changed from 1 to 2'
  

  Parameters

  eventInfo : EventInfo

  An object containing information about the fired event.

  name : string

  The property name.

  value : TValue

  The new property value.

  oldValue : TValue

  The previous property value.

• set:{property}( eventInfo, name, value, oldValue )module:utils/observablemixin~Observable#event:set:{property}

  See source

  Fired when a property value is going to be set but is not set yet (before the change event is fired).

  You can control the final value of the property by using the event's return property.

  observable.set( 'prop', 1 );
  
  observable.on<ObservableSetEvent<number>>( 'set:prop', ( evt, propertyName, newValue, oldValue ) => {
  	console.log( `Value is going to be changed from ${ oldValue } to ${ newValue }` );
  	console.log( `Current property value is ${ observable[ propertyName ] }` );
  
  	// Let's override the value.
  	evt.return = 3;
  } );
  
  observable.on<ObservableChangeEvent<number>>( 'change:prop', ( evt, propertyName, newValue, oldValue ) => {
  	console.log( `Value has changed from ${ oldValue } to ${ newValue }` );
  } );
  
  observable.prop = 2; // -> 'Value is going to be changed from 1 to 2'
                       // -> 'Current property value is 1'
                       // -> 'Value has changed from 1 to 3'
  

  Note: The event is fired even when the new value is the same as the old value.

  Parameters

  eventInfo : EventInfo

  An object containing information about the fired event.

  name : string

  The property name.

  value : TValue

  The new property value.

  oldValue : TValue

  The previous property value.