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Class

View (engine/view)

@ckeditor/ckeditor5-engine/src/view/view

class

Editor's view controller class. Its main responsibility is DOM - View management for editing purposes, to provide abstraction over the DOM structure and events and hide all browsers quirks.

View controller renders view document to DOM whenever view structure changes. To determine when view can be rendered, all changes need to be done using the change method, using DowncastWriter:

view.change( writer => {
    writer.insert( position, writer.createText( 'foo' ) );
} );

View controller also register observers which observes changes on DOM and fire events on the Document. Note that the following observers are added by the class constructor and are always available:

This class also binds the DOM and the view elements.

If you do not need full a DOM - view management, and only want to transform a tree of view elements to a tree of DOM elements you do not need this controller. You can use the DomConverter instead.

Filtering

Properties

  • document : Document

    readonly

    Instance of the Document associated with this view controller.

  • domConverter : DomConverter

    readonly

    Instance of the domConverter use by renderer and observers.

  • domRoots : Map

    readonly

    Roots of the DOM tree. Map on the HTMLElements with roots names as keys.

  • _renderingDisabled : Boolean

    protected

    Internal flag to temporary disable rendering. See usage in the editing controller.

  • renderer : Renderer

    protected

    Instance of the renderer.

  • _observers : Map.<Function, Observer>

    private

    Map of registered observers.

  • _ongoingChange : Boolean

    private

    Is set to true when view changes are currently in progress.

  • _renderingInProgress : Boolean

    private

    Used to prevent calling render and change during rendering view to the DOM.

  • _writer : DowncastWriter

    private

    DowncastWriter instance used in {@link #change change method) callbacks.

Methods

  • addObserver( Observer ) → Observer

    Creates observer of the given type if not yet created, enables it and attaches to all existing and future DOM roots.

    Note: Observers are recognized by their constructor (classes). A single observer will be instantiated and used only when registered for the first time. This means that features and other components can register a single observer multiple times without caring whether it has been already added or not.

    Parameters

    Observer : function

    The constructor of an observer to add. Should create an instance inheriting from Observer.

    Returns

    Observer

    Added observer instance.

  • attachDomRoot( domRoot, [ name ] )

    Attaches DOM root element to the view element and enable all observers on that element. Also mark element to be synchronized with the view what means that all child nodes will be removed and replaced with content of the view root.

    This method also will change view element name as the same as tag name of given dom root. Name is always transformed to lower case.

    Parameters

    domRoot : Element

    DOM root element.

    [ name ] : String

    Name of the root.

    Defaults to 'main'

  • bind( bindProperties ) → Object

    Binds obvervable properties to other objects implementing the Observable interface.

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

    Let's 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 );

    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 : String

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

    Returns

    Object

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

  • change( callback ) → *

    The change() method is the primary way of changing the view. You should use it to modify any node in the view tree. It makes sure that after all changes are made the view is rendered to the DOM. It prevents situations when the DOM is updated when the view state is not yet correct. It allows to nest calls one inside another and still performs a single rendering after all those changes are made. It also returns the return value of its callback.

    const text = view.change( writer => {
        const newText = writer.createText( 'foo' );
        writer.insert( position1, newText );
    
        view.change( writer => {
            writer.insert( position2, writer.createText( 'bar' ) );
        } );
    
        writer.remove( range );
    
        return newText;
    } );

    When the outermost change block is done and rendering to the DOM is over the View#render event is fired.

    This method throws a applying-view-changes-on-rendering error when the change block is used after rendering to the DOM has started.

    Parameters

    callback : function

    Callback function which may modify the view.

    Returns

    *

    Value returned by the callback.

  • createPositionAfter( item ) → Position

    Creates a new position after given view item.

    Parameters

    item : Item

    View item after which the position should be located.

    Returns

    Position
  • createPositionAt( itemOrPosition, [ offset ] )

    Creates position at the given location. The location can be specified as:

    • a position,
    • parent element and offset (offset defaults to 0),
    • parent element and 'end' (sets position at the end of that element),
    • view item and 'before' or 'after' (sets position before or after given view item).

    This method is a shortcut to other constructors such as:

    Parameters

    itemOrPosition : Item | Position
    [ offset ] : Number | 'end' | 'before' | 'after'

    Offset or one of the flags. Used only when first parameter is a view item.

  • createPositionBefore( item ) → Position

    Creates a new position before given view item.

    Parameters

    item : Item

    View item before which the position should be located.

    Returns

    Position
  • createRange( start, [ end ] ) → Range

    Creates a range spanning from start position to end position.

    Note: This factory method creates it's own Position instances basing on passed values.

    Parameters

    start : Position

    Start position.

    [ end ] : Position

    End position. If not set, range will be collapsed at start position.

    Returns

    Range
  • createRangeIn( element ) → Range

    Creates a range inside an element which starts before the first child of that element and ends after the last child of that element.

    Parameters

    element : Element

    Element which is a parent for the range.

    Returns

    Range
  • createRangeOn( item ) → Range

    Creates a range that starts before given view item and ends after it.

    Parameters

    item : Item

    Returns

    Range
  • createSelection( [ selectable ], [ placeOrOffset ], [ options ] = { [options.backward], [options.fake], [options.label] } ) → Selection

    Creates new Selection instance.

    // Creates empty selection without ranges.
    const selection = view.createSelection();
    
    // Creates selection at the given range.
    const range = view.createRange( start, end );
    const selection = view.createSelection( range );
    
    // Creates selection at the given ranges
    const ranges = [ view.createRange( start1, end2 ), view.createRange( star2, end2 ) ];
    const selection = view.createSelection( ranges );
    
    // Creates selection from the other selection.
    const otherSelection = view.createSelection();
    const selection = view.createSelection( otherSelection );
    
    // Creates selection from the document selection.
    const selection = view.createSelection( editor.editing.view.document.selection );
    
    // Creates selection at the given position.
    const position = view.createPositionFromPath( root, path );
    const selection = view.createSelection( position );
    
    // Creates collapsed selection at the position of given item and offset.
    const paragraph = view.createContainerElement( 'paragraph' );
    const selection = view.createSelection( paragraph, offset );
    
    // Creates a range inside an element which starts before the
    // first child of that element and ends after the last child of that element.
    const selection = view.createSelection( paragraph, 'in' );
    
    // Creates a range on an item which starts before the item and ends
    // just after the item.
    const selection = view.createSelection( paragraph, 'on' );

    Selection's factory method allow passing additional options (backward, fake and label) as the last argument.

    // Creates backward selection.
    const selection = view.createSelection( range, { backward: true } );

    Fake selection does not render as browser native selection over selected elements and is hidden to the user. This way, no native selection UI artifacts are displayed to the user and selection over elements can be represented in other way, for example by applying proper CSS class.

    Additionally fake's selection label can be provided. It will be used to describe fake selection in DOM (and be properly handled by screen readers).

    // Creates fake selection with label.
    const selection = view.createSelection( range, { fake: true, label: 'foo' } );

    Parameters

    [ selectable ] : Selection | DocumentSelection | Position | Iterable.<Range> | Range | Item | null
    [ placeOrOffset ] : Number | 'before' | 'end' | 'after' | 'on' | 'in'

    Offset or place when selectable is an Item.

    [ options ] : Object
    Properties
    [ options.backward ] : Boolean

    Sets this selection instance to be backward.

    [ options.fake ] : Boolean

    Sets this selection instance to be marked as fake.

    [ options.label ] : String

    Label for the fake selection.

    Returns

    Selection
  • decorate( methodName )

    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 {
        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: 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 : String

    Name of the method to decorate.

  • delegate( events ) → EmitterMixinDelegateChain

    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
  • destroy()

    Destroys this instance. Makes sure that all observers are destroyed and listeners removed.

  • disableObservers()

    Disables all added observers.

  • enableObservers()

    Enables all added observers.

  • fire( eventOrInfo, [ args ] ) → *

    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).

  • focus()

    It will focus DOM element representing EditableElement that is currently having selection inside.

  • getDomRoot( [ name ] ) → Element

    Gets DOM root element.

    Parameters

    [ name ] : String

    Name of the root.

    Defaults to 'main'

    Returns

    Element

    DOM root element instance.

  • getObserver( Observer ) → Observer | undefined

    Returns observer of the given type or undefined if such observer has not been added yet.

    Parameters

    Observer : function

    The constructor of an observer to get.

    Returns

    Observer | undefined

    Observer instance or undefined.

  • listenTo( emitter, event, callback, [ options ] = { [options.priority] } )

    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 )

    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] } )

    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] } )

    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 {}

  • render()

    Renders view document to DOM. If any view changes are currently in progress, rendering will start after all change blocks are processed.

    Throws CKEditorError applying-view-changes-on-rendering when trying to re-render when rendering to DOM has already started.

  • scrollToTheSelection()

    Scrolls the page viewport and domRoots with their ancestors to reveal the caret, if not already visible to the user.

  • set( name, [ value ] )

    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 ] )

    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 ] )

    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 ] )

    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 ] : String

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

  • _render()

    private

    Renders all changes. In order to avoid triggering the observers (e.g. mutations) all observers are disabled before rendering and re-enabled after that.

Events

  • change:{property}( eventInfo, name, value, oldValue )

    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.

  • render( eventInfo )

    Fired after a topmost change block and all post-fixers are executed.

    Actual rendering is performed as a first listener on 'normal' priority.

    view.on( 'render', () => {
        // Rendering to the DOM is complete.
    } );

    This event is useful when you want to update interface elements after the rendering, e.g. position of the balloon panel. If you wants to change view structure use post-fixers.

    Parameters

    eventInfo : EventInfo

    An object containing information about the fired event.

  • set:{property}( eventInfo, name, value, oldValue )

    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.