Observable (utils)

@ckeditor/ckeditor5-utils/src/observablemixin

Methods

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

  Binds observable properties to another objects implementing Observable interface (like Model).

  Once bound, the observable will immediately share the current state of properties of the observable it is bound to and react to the changes to these properties in the future.

  Note: To release the binding use unbind.

  Using bind().to() chain:

  A.bind( 'a' ).to( B );
  A.bind( 'a' ).to( B, 'b' );
  A.bind( 'a', 'b' ).to( B, 'c', 'd' );
  A.bind( 'a' ).to( B, 'b', C, 'd', ( b, d ) => b + d );

  It is also possible to bind to the same property in a observables collection using bind().toMany() chain:

  A.bind( 'a' ).toMany( [ B, C, D ], 'x', ( a, b, c ) => a + b + c );
  A.bind( 'a' ).toMany( [ B, C, D ], 'x', ( ...x ) => x.every( x => x ) );

  Parameters

  bindProperties : String

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

  Returns

  Object

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

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

  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.

  This is a very simplified method decoration. Itself it doesn't change the behavior of a method (expect adding the event), but it allows to modify it later on by listening to the method's event.

  For example, in order to cancel the method execution one can stop the event:

  class Foo {
      constructor() {
          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: we used a high priority listener here to execute this callback before the one which calls the original method (which used the default priority).

  It's also possible to change the return value:

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

  Finally, it's possible to access and modify the parameters:

  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 : String

  Name of the method to decorate.

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

  inherited

  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 : String

  Event names that will be delegated to another emitter.

  Returns

  EmitterMixinDelegateChain

• fire( eventOrInfo, [ args ] ) → *module:utils/observablemixin~Observable#fire

  inherited

  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.

  Parameters

  eventOrInfo : String | EventInfo

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

  [ args ] : *

  Additional arguments to be passed to the callbacks.

  Returns

  *

  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).

• listenTo( emitter, event, callback, [ options ] = { [options.priority] } )module:utils/observablemixin~Observable#listenTo

  inherited

  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.

  Parameters

  emitter : Emitter

  The object that fires the event.

  event : String

  The name of the event.

  callback : function

  The function to be called on event.

  [ options ] : Object

  Additional options.

  Properties

  [ options.priority ] : PriorityString | Number

  The priority of this event callback. The higher the priority value the sooner the callback will be fired. Events having the same priority are called in the order they were added.

  Defaults to 'normal'

  Defaults to {}

• off( event, callback )module:utils/observablemixin~Observable#off

  inherited

  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.

• on( event, callback, [ options ] = { [options.priority] } )module:utils/observablemixin~Observable#on

  inherited

  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).

  Parameters

  event : String

  The name of the event.

  callback : function

  The function to be called on event.

  [ options ] : Object

  Additional options.

  Properties

  [ options.priority ] : PriorityString | Number

  The priority of this event callback. The higher the priority value the sooner the callback will be fired. Events having the same priority are called in the order they were added.

  Defaults to 'normal'

  Defaults to {}

• once( event, callback, [ options ] = { [options.priority] } )module:utils/observablemixin~Observable#once

  inherited

  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.

  Parameters

  event : String

  The name of the event.

  callback : function

  The function to be called on event.

  [ options ] : Object

  Additional options.

  Properties

  [ options.priority ] : PriorityString | Number

  The priority of this event callback. The higher the priority value the sooner the callback will be fired. Events having the same priority are called in the order they were added.

  Defaults to 'normal'

  Defaults to {}

• set( name, [ value ] )module:utils/observablemixin~Observable#set

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

  It accepts also 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 have 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.

  Parameters

  name : String | Object

  The property's name or object with name=>value pairs.

  [ value ] : *

  The property's value (if name was passed in the first parameter).

• stopDelegating( [ event ], [ emitter ] )module:utils/observablemixin~Observable#stopDelegating

  inherited

  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.

• stopListening( [ emitter ], [ event ], [ callback ] )module:utils/observablemixin~Observable#stopListening

  inherited

  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.

• unbind( [ unbindProperties ] )module:utils/observablemixin~Observable#unbind

  Removes the binding created with bind.

  A.unbind( 'a' );
  A.unbind();

  Parameters

  [ unbindProperties ] : String

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

Events

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

  Fired when a property changed value.

  observable.set( 'prop', 1 );
  
  observable.on( '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 : *

  The new property value.

  oldValue : *

  The previous property value.

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

  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( '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( '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: 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 : *

  The new property value.

  oldValue : *

  The previous property value.