Undo (undo)

@ckeditor/ckeditor5-undo/src/undo

class

The undo feature.

This is a "glue" plugin which loads the undo editing feature and undo UI feature.

Below is the explanation of the undo mechanism working together with History:

Whenever a operation is applied to the document, it is saved to History as is. The batch that owns that operation is also saved, in UndoCommand, together with the selection that was present in the document before the operation was applied. A batch is saved instead of the operation because changes are undone batch-by-batch, not operation-by-operation and a batch is seen as one undo step.

After some changes happen to the document, the History and UndoCommand stack can be represented as follows:

    History                            Undo stack
==============             ==================================
[operation A1]                         [batch A]
[operation B1]                         [batch B]
[operation B2]                         [batch C]
[operation C1]
[operation C2]
[operation B3]
[operation C3]

Where operations starting with the same letter are from same batch.

Undoing a batch means that a set of operations which will reverse the effects of that batch needs to be generated. For example, if a batch added several letters, undoing the batch should remove them. It is important to apply undoing operations in the reversed order, so if a batch has operation X, Y, Z, reversed operations Zr, Yr and Xr need to be applied. Otherwise reversed operation Xr would operate on a wrong document state, because operation X does not know that operations Y and Z happened.

After operations from an undone batch got reversed, one needs to make sure if they are ready to be applied. In the scenario above, operation C3 is the last operation and C3r bases on up-to-date document state, so it can be applied to the document.

     History                             Undo stack
=================             ==================================
[ operation A1  ]                      [  batch A  ]
[ operation B1  ]                      [  batch B  ]
[ operation B2  ]             [   processing undoing batch C   ]
[ operation C1  ]
[ operation C2  ]
[ operation B3  ]
[ operation C3  ]
[ operation C3r ]

Next is operation C2, reversed to C2r. C2r bases on C2, so it bases on the wrong document state. It needs to be transformed by operations from history that happened after it, so it "knows" about them. Let us assume that C2' = C2r * B3 * C3 * C3r, where * means "transformed by". Rest of operations from that batch are processed in the same fashion.

     History                             Undo stack                                      Redo stack
=================             ==================================             ==================================
[ operation A1  ]                      [  batch A  ]                                    [ batch Cr ]
[ operation B1  ]                      [  batch B  ]
[ operation B2  ]
[ operation C1  ]
[ operation C2  ]
[ operation B3  ]
[ operation C3  ]
[ operation C3r ]
[ operation C2' ]
[ operation C1' ]

Selective undo works on the same basis, however, instead of undoing the last batch in the undo stack, any batch can be undone. The same algorithm applies: operations from a batch (i.e. A1) are reversed and then transformed by operations stored in history.

Redo also is very similar to undo. It has its own stack that is filled with undoing (reversed batches). Operations from batch that is re-done are reversed-back, transformed in proper order and applied to the document.

     History                             Undo stack                                      Redo stack
=================             ==================================             ==================================
[ operation A1  ]                      [  batch A  ]
[ operation B1  ]                      [  batch B  ]
[ operation B2  ]                      [ batch Crr ]
[ operation C1  ]
[ operation C2  ]
[ operation B3  ]
[ operation C3  ]
[ operation C3r ]
[ operation C2' ]
[ operation C1' ]
[ operation C1'r]
[ operation C2'r]
[ operation C3rr]

Filtering

Public
Inherited
Mixed
Protected
Private
Deprecated

Properties

editor : Editor

readonly inherited
The editor instance.
Note that most editors implement the EditorWithUI interface in addition to the base Editor interface. However, editors with an external UI (i.e. Bootstrap-based) or a headless editor may not implement the EditorWithUI interface.

Because of above, to make plugins more universal, it is recommended to split features into:
- The "editing" part that only uses the Editor interface.
- The "UI" part that uses both the Editor interface and the EditorWithUI interface.

Static properties

pluginName : String | undefined

readonly inherited static
An optional name of the plugin. If set, the plugin will be available in get by its name and its constructor. If not, then only by its constructor.
The name should reflect the constructor name.

To keep the plugin class definition tight it is recommended to define this property as a static getter:
```
export default class ImageCaption {
    static get pluginName() {
        return 'ImageCaption';
    }
}
```
Note: The native Function.name property could not be used to keep the plugin name because it will be mangled during code minification.

Naming a plugin is necessary to enable removing it through the config.removePlugins option.
requires : Array.<Function> | undefined

readonly inherited static
An array of plugins required by this plugin.
To keep the plugin class definition tight it is recommended to define this property as a static getter:
```
import Image from './image.js';

export default class ImageCaption {
    static get requires() {
        return [ Image ];
    }
}
```

Methods

constructor( editor )

inherited

Creates a new plugin instance. This is the first step of the plugin initialization. See also init and afterInit.

A plugin is always instantiated after its dependencies and the init and afterInit methods are called in the same order.

Usually, you will want to put your plugin's initialization code in the init method. The constructor can be understood as "before init" and used in special cases, just like afterInit serves the special "after init" scenarios (e.g.the code which depends on other plugins, but which does not explicitly require them).

Parameters

editor : Editor
afterInit() → null | Promise

inherited

The third (and last) stage of plugin initialization. See also constructor and init.

Note: This method is optional. A plugin instance does not need to have it defined.

Returns

null | Promise
bind( bindProperties ) → Object

inherited
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 )

inherited
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 ) → EmitterMixinDelegateChain

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
destroy() → null | Promise

inherited

Destroys the plugin.

Note: This method is optional. A plugin instance does not need to have it defined.

Returns

null | Promise
fire( eventOrInfo, [ args ] ) → *

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).
init() → null | Promise

inherited

The second stage (after plugin constructor) of plugin initialization. Unlike the plugin constructor this method can be asynchronous.

A plugin's init() method is called after its dependencies are initialized, so in the same order as constructors of these plugins.

Note: This method is optional. A plugin instance does not need to have it defined.

Returns

null | Promise
listenTo( emitter, event, callback, [ options ] = { [options.priority] } )

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 )

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] } )

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] } )

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 ] )

inherited

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 ] )

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 ] )

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 ] )

inherited
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 )

inherited
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 )

inherited
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.

Undo (undo)

Filtering

Properties

editor : Editormodule:undo/undo~Undo#editor

Static properties

pluginName : String | undefinedmodule:undo/undo~Undo.pluginName

requires : Array.<Function> | undefinedmodule:undo/undo~Undo.requires

Methods

constructor( editor )module:undo/undo~Undo#constructor

Parameters

afterInit() → null | Promisemodule:undo/undo~Undo#afterInit

Returns

bind( bindProperties ) → Objectmodule:undo/undo~Undo#bind

Parameters

Returns

decorate( methodName )module:undo/undo~Undo#decorate

Parameters

delegate( events ) → EmitterMixinDelegateChainmodule:undo/undo~Undo#delegate

Parameters

Returns

destroy() → null | Promisemodule:undo/undo~Undo#destroy

Returns

fire( eventOrInfo, [ args ] ) → *module:undo/undo~Undo#fire

Parameters

Returns

init() → null | Promisemodule:undo/undo~Undo#init

Returns

listenTo( emitter, event, callback, [ options ] = { [options.priority] } )module:undo/undo~Undo#listenTo

Parameters

off( event, callback )module:undo/undo~Undo#off

Parameters

on( event, callback, [ options ] = { [options.priority] } )module:undo/undo~Undo#on

Parameters

once( event, callback, [ options ] = { [options.priority] } )module:undo/undo~Undo#once

Parameters

set( name, [ value ] )module:undo/undo~Undo#set

Parameters

stopDelegating( [ event ], [ emitter ] )module:undo/undo~Undo#stopDelegating

Parameters

stopListening( [ emitter ], [ event ], [ callback ] )module:undo/undo~Undo#stopListening

Parameters

unbind( [ unbindProperties ] )module:undo/undo~Undo#unbind

Parameters

Events

change:{property}( eventInfo, name, value, oldValue )module:undo/undo~Undo#event:change:{property}

Parameters

set:{property}( eventInfo, name, value, oldValue )module:undo/undo~Undo#event:set:{property}

Parameters

`editor : Editor`

`pluginName : String | undefined`

`requires : Array.<Function> | undefined`

`constructor( editor )`

`afterInit() → null | Promise`

`bind( bindProperties ) → Object`

`decorate( methodName )`

`delegate( events ) → EmitterMixinDelegateChain`

`destroy() → null | Promise`

`fire( eventOrInfo, [ args ] ) → *`

`init() → null | Promise`

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

`off( event, callback )`

`on( event, callback, [ options ] = { [options.priority] } )`

`once( event, callback, [ options ] = { [options.priority] } )`

`set( name, [ value ] )`

`stopDelegating( [ event ], [ emitter ] )`

`stopListening( [ emitter ], [ event ], [ callback ] )`

`unbind( [ unbindProperties ] )`

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

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