title: Watchdog
Every non-trivial piece of software has bugs. Despite our high quality standards like 100% code coverage, regression testing and manual tests before every release, CKEditor 5 is not free of bugs. Neither is the browser used by the user, your application in which CKEditor 5 is integrated, or any third-party addons that you used.
In order to limit the effect of an editor crash on the user experience, you can automatically restart the WYSIWYG editor with the content saved just before the crash.
The {@link module:watchdog/watchdog~Watchdog} utility allows you to do exactly that. It ensures that an editor instance is running, despite a potential crash. It works by detecting that an editor crashed, destroying it, and automatically creating a new instance of that editor with the content of the previous editor.
It should be noticed that the most "dangerous" places in the API - like editor.model.change(), editor.editing.view.change(), emitters - are covered with checks and try-catch blocks that allow detecting unknown errors and restart editor when they occur.
There are two available types of watchdogs:
Context.
Note: a watchdog can be used only with an {@link builds/guides/integration/advanced-setup#scenario-2-building-from-source editor built from source}.
Install the @ckeditor/ckeditor5-watchdog package:
npm install --save @ckeditor/ckeditor5-watchdog
Then, change your ClassicEditor.create() call to watchdog.create() as follows:
import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
import EditorWatchdog from '@ckeditor/ckeditor5-watchdog/src/editorwatchdog';
import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
// Create a watchdog for the given editor type.
const watchdog = new EditorWatchdog( ClassicEditor );
// Create a new editor instance.
watchdog.create( document.querySelector( '#editor' ), {
plugins: [ Essentials, Paragraph, Bold, Italic ],
toolbar: [ 'bold', 'italic', 'alignment' ]
} );
In other words, your goal is to create a watchdog instance and make the watchdog create an instance of the editor you want to use. The watchdog will then create a new editor and if it ever crashes, restart it by creating a new editor.
A new editor instance is created every time the watchdog detects a crash. Thus, the editor instance should not be kept in your application's state. Use the {@link module:watchdog/editorwatchdog~EditorWatchdog#editor `EditorWatchdog#editor`} property instead.
It also means that any code that should be executed for any new editor instance should be either loaded as an editor plugin or executed in the callbacks defined using {@link module:watchdog/editorwatchdog~EditorWatchdog#setCreator `EditorWatchdog#setCreator()`} and {@link module:watchdog/editorwatchdog~EditorWatchdog#setDestructor `EditorWatchdog#setDestructor()`}. Read more about controlling the editor creation and destruction in the next section.
For more control over the creation and destruction of editor instances, you can use {@link module:watchdog/editorwatchdog~EditorWatchdog#setCreator EditorWatchdog#setCreator()} and, if needed, the {@link module:watchdog/editorwatchdog~EditorWatchdog#setDestructor EditorWatchdog#setDestructor()}:
// Create editor watchdog.
const watchdog = new EditorWatchdog();
// Define a callback that will create an editor instance and return it.
watchdog.setCreator( ( elementOrData, editorConfig ) => {
return ClassicEditor
.create( elementOrData, editorConfig )
.then( editor => {
// Do something with the new editor instance.
} );
} );
// Do something before the editor is destroyed. Return a promise.
watchdog.setDestructor( editor => {
// ...
return editor
.destroy()
.then( () => {
// Do something after the editor is destroyed.
} );
} );
// Create editor instance and start watching it.
watchdog.create( elementOrData, editorConfig );
The default (not overridden ny `setDestructor()`) editor destructor simply executes `Editor#destroy()`.
Other useful {@link module:watchdog/editorwatchdog~EditorWatchdog methods, properties and events}:
watchdog.on( 'error', () => { console.log( 'Editor crashed.' ) } );
watchdog.on( 'restart', () => { console.log( 'Editor was restarted.' ) } );
// Destroy the watchdog and the current editor instance.
watchdog.destroy();
// The current editor instance.
watchdog.editor;
// The current state of the editor.
// The editor might be in one of the following states:
//
// * `initializing` - before the first initialization, and after crashes, before the editor is ready,
// * `ready` - a state when a user can interact with the editor,
// * `crashed` - a state when an error occurs - it quickly changes to `initializing` or `crashedPermanently` depending on how many and how frequency errors have been caught recently,
// * `crashedPermanently` - a state when the watchdog stops reacting to errors and keeps the editor crashed,
// * `destroyed` - a state when the editor is manually destroyed by the user after calling `watchdog.destroy()`.
//
// This property is observable.
watchdog.state;
// Listen to state changes.
watchdog.on( 'change:state' ( evt, name, currentState, prevState ) => {
console.log( `State changed from ${ currentState } to ${ prevState }` );
if ( currentState === 'crashedPermanently' ) {
watchdog.editor.isReadOnly = true;
}
} );
// An array of editor crashes info.
watchdog.crashes.forEach( crashInfo => console.log( crashInfo ) );
Install the @ckeditor/ckeditor5-watchdog package:
npm install --save @ckeditor/ckeditor5-watchdog
And then change your editor and context initialization code:
import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
import ContextWatchdog from '@ckeditor/ckeditor5-watchdog/src/contextwatchdog';
import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
import Context from '@ckeditor/ckeditor5-core/src/context';
// Create a context watchdog and pass the `Context` class with optional watchdog configuration:
const watchdog = new ContextWatchdog( Context, {
crashNumberLimit: 10
} );
// Initialize the watchdog with context configuration:
await watchdog.create( {
plugins: [
// ...
],
// ...
} );
// Add editor instances.
// You mat also use multiple `ContextWatchdog#add()` calls, each adding a single editor.
await watchdog.add( [ {
id: 'editor1',
type: 'editor',
sourceElementOrData: document.querySelector( '#editor' ),
config: {
plugins: [ Essentials, Paragraph, Bold, Italic ],
toolbar: [ 'bold', 'italic', 'alignment' ]
},
creator: ( element, config ) => ClassicEditor.create( element, config )
}, {
id: 'editor2',
type: 'editor',
sourceElementOrData: document.querySelector( '#editor' ),
config: {
plugins: [ Essentials, Paragraph, Bold, Italic ],
toolbar: [ 'bold', 'italic', 'alignment' ]
},
creator: ( element, config ) => ClassicEditor.create( element, config )
} ] );
// Or:
await watchdog.add( {
id: 'editor1',
type: 'editor',
sourceElementOrData: document.querySelector( '#editor' ),
config: {
plugins: [ Essentials, Paragraph, Bold, Italic ],
toolbar: [ 'bold', 'italic', 'alignment' ]
},
creator: ( element, config ) => ClassicEditor.create( element, config )
} );
await watchdog.add( {
id: 'editor2',
type: 'editor',
sourceElementOrData: document.querySelector( '#editor' ),
config: {
plugins: [ Essentials, Paragraph, Bold, Italic ],
toolbar: [ 'bold', 'italic', 'alignment' ]
},
creator: ( element, config ) => ClassicEditor.create( element, config )
} );
To destroy one of the item instances use {@link module:watchdog/contextwatchdog~ContextWatchdog#remove ContextWatchdog#remove}:
await watchdog.remove( [ 'editor1', 'editor2' ] );
// Or:
await watchdog.remove( 'editor1' );
await watchdog.remove( 'editor2' );
Examples presents the "synchronous way" of the integration with the context watchdog feature, however it's not needed to wait for the promises returned by the `create()`, `add()` and `remove()` methods. There might be a need
to create and destroy items dynamically with shared context and that can be easily achieved as all promises operating on the internal API will be chained.
The context watchdog feature provides the following API:
// Creating watchdog that will use the `Context` class and watchdog configuration.
const watchdog = new ContextWatchdog( Context, watchdogConfig );
// Setting a custom creator for the context.
watchdog.setCreator( async config => {
const context = await Context.create( config ) );
// Do something when the context is initialized.
return context;
} );
// Setting a custom destructor for the context.
watchdog.setDestructor( async context => {
// Do something before destroy.
await context.destroy();
} );
// Initializing the context watchdog with the context configuration.
await watchdog.create( contextConfig );
// Adding item configuration (or an array of item configurations).
await watchdog.add( {
id: 'editor1',
type: 'editor',
sourceElementOrData: domElementOrEditorData
config: editorConfig,
creator: createEditor,
destructor: destroyEditor,
} );
await watchdog.add( [
{
id: 'editor1',
type: 'editor',
sourceElementOrData: domElementOrEditorData
config: editorConfig,
creator: createEditor,
destructor: destroyEditor,
},
// ...
] );
// Remove and destroy given item (or items).
await watchdog.remove( 'editor1' );
await watchdog.remove( [ 'editor1', 'editor2', ... ] );
// Getting given item instance.
const editor1 = watchdog.get( 'editor1' );
// Getting given item state.
const editor1State = watchdog.getState( 'editor1' );
// Getting the context state.
const contextState = watchdog.state;
// The `error` event is fired when the context watchdog catches a context-related error.
// Note that errors fired by items are not delegated to `ContextWatchdog#event:error`.
// See also `ContextWatchdog#event:itemError`.
watchdog.on( 'error', ( evt, { error } ) => {
console.log( 'The context crashed.' );
} );
// The `restart` event is fired when the context is set back to the `ready` state (after it was in `error` state).
// Similarly, this event is not thrown for internal item restarts.
watchdog.on( 'restart', () => {
console.log( 'The context has been restarted.' );
} );
// The `itemError` event is fired when an error occurred in one of the added items.
watchdog.on( 'itemError', ( evt, { error, itemId } ) => {
console.log( `An error occurred in an item with the '${ itemId }' id.` );
} );
// The `itemRestart` event is fired when an item is set back to the `ready` state (after it was in `error` state).
watchdog.on( 'itemRestart', ( evt, { itemId } ) => {
console.log( 'An item with '${ itemId }' id has been restarted.' );
} );
Both {@link module:watchdog/editorwatchdog~EditorWatchdog#constructor EditorWatchdog} and {@link module:watchdog/contextwatchdog~ContextWatchdog#constructor ContextWatchdog} constructors accept a {{@link module:watchdog/watchdog~WatchdogConfig configuration object} as the second argument with the following optional properties:
crashNumberLimit - A threshold specifying the number of errors (defaults to 3). After this limit is reached and the time between last errors is shorter than minimumNonErrorTimePeriod the watchdog changes its state to crashedPermanently and it stops restarting the editor. This prevents an infinite restart loop.minimumNonErrorTimePeriod - An average amount of milliseconds between last editor errors (defaults to 5000). When the period of time between errors is lower than that and the crashNumberLimit is also reachedm the watchdog changes its state to crashedPermanently and it stops restarting the editor. This prevents an infinite restart loop.saveInterval - A minimum number of milliseconds between saving editor data internally (defaults to 5000). Note that for large documents this might have an impact on the editor performance.const editorWatchdog = new EditorWatchdog( ClassicEditor, {
minimumNonErrorTimePeriod: 2000,
crashNumberLimit: 4,
saveInterval: 1000
} );
Note that the context watchdog passes its configuration to editor watchdogs that it creates for added editors.
The watchdogs do not handle errors thrown during the editor or context initialization (e.g. in Editor.create()) and editor destruction (e.g. in Editor#destroy()). Errors thrown at these stages mean that there is a problem in the code integrating the editor with your application and such problem cannot be fixed by restarting the editor.