Third–party UI

// Basic classes to create an editor.
import Editor from '@ckeditor/ckeditor5-core/src/editor/editor';
import EditorUI from '@ckeditor/ckeditor5-core/src/editor/editorui';
import EditorUIView from '@ckeditor/ckeditor5-ui/src/editorui/editoruiview';
import FocusTracker from '@ckeditor/ckeditor5-utils/src/focustracker';
import ComponentFactory from '@ckeditor/ckeditor5-ui/src/componentfactory';
import InlineEditableUIView from '@ckeditor/ckeditor5-ui/src/editableui/inline/inlineeditableuiview';
import ElementReplacer from '@ckeditor/ckeditor5-utils/src/elementreplacer';

// Interfaces to extend the basic Editor API.
import DataApiMixin from '@ckeditor/ckeditor5-core/src/editor/utils/dataapimixin';
import ElementApiMixin from '@ckeditor/ckeditor5-core/src/editor/utils/elementapimixin';

// Helper function for adding interfaces to the Editor class.
import mix from '@ckeditor/ckeditor5-utils/src/mix';

// Helper function that gets the data from an HTML element that the Editor is attached to.
import getDataFromElement from '@ckeditor/ckeditor5-utils/src/dom/getdatafromelement';

// Helper function that binds the editor with an HTMLForm element.
import attachToForm from '@ckeditor/ckeditor5-core/src/editor/utils/attachtoform';

// Basic features that every editor should enable.
import Clipboard from '@ckeditor/ckeditor5-clipboard/src/clipboard';
import Enter from '@ckeditor/ckeditor5-enter/src/enter';
import Typing from '@ckeditor/ckeditor5-typing/src/typing';
import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
import UndoEditing from '@ckeditor/ckeditor5-undo/src/undoengine';

// Basic features associated with the edited content.
import BoldEditing from '@ckeditor/ckeditor5-basic-styles/src/bold/boldediting';
import ItalicEditing from '@ckeditor/ckeditor5-basic-styles/src/italic/italicediting';
import UnderlineEditing from '@ckeditor/ckeditor5-basic-styles/src/underline/underlineediting';
import HeadingEditing from '@ckeditor/ckeditor5-heading/src/heading/headingediting';

// Extending the Editor class, which brings the base editor API.
export default class BootstrapEditor extends Editor {
    constructor( element, config ) {
        super( config );

        // Remember the element the editor is created with.
        this.sourceElement = element;

        // Create the ("main") root element of the model tree.
        this.model.document.createRoot();

        // The UI layer of the editor.
        this.ui = new BootstrapEditorUI( this );

        // When editor#element is a textarea inside a form element,
        // the content of this textarea will be updated on form submit.
        attachToForm( this );
    }

    destroy() {
        // When destroyed, the editor sets the output of editor#getData() into editor#element...
        this.updateSourceElement();

        // ...and destroys the UI.
        this.ui.destroy();

        return super.destroy();
    }

    static create( element, config ) {
        return new Promise( resolve => {
            const editor = new this( element, config );

            resolve(
                editor.initPlugins()
                    // Initialize the UI first. See the BootstrapEditorUI class to learn more.
                    .then( () => editor.ui.init( element ) )
                    // Fill the editable with the initial data.
                    .then( () => editor.data.init( getDataFromElement( element ) ) )
                    // Fire the `editor#ready` event that announce the editor is complete and ready to use.
                    .then( () => editor.fire( 'ready' ) )
                    .then( () => editor )
            );
        } );
    }
}

// Mixing interfaces, which extends the basic editor API.
mix( BootstrapEditor, DataApiMixin );
mix( BootstrapEditor, ElementApiMixin );

<!-- The outermost cotainer of the editor. -->
<div class="ck-editor">
    <!-- The toolbar of the editor. -->
    <div class="btn-toolbar" role="toolbar" aria-label="Editor toolbar">
        <!-- The headings dropdown. -->
        <div class="btn-group mr-2" role="group" aria-label="Headings">
            <div class="dropdown" id="heading">
              <button class="btn btn-primary btn-sm dropdown-toggle" type="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"><span>Headings</span></button>
              <div class="dropdown-menu" aria-labelledby="heading-button"></div>
            </div>
        </div>

        <!-- Basic styles buttons. -->
        <div class="btn-group mr-2" role="group" aria-label="Basic styles">
            <button type="button" class="btn btn-primary btn-sm" id="bold">B</button>
            <button type="button" class="btn btn-primary btn-sm" id="italic">I</button>
            <button type="button" class="btn btn-primary btn-sm" id="underline">U</button>
        </div>

        <!-- Undo and redo buttons. -->
        <div class="btn-group mr-2" role="group" aria-label="Undo">
            <button type="button" class="btn btn-primary btn-sm" id="undo">&larr;</button>
            <button type="button" class="btn btn-primary btn-sm" id="redo">&rarr;</button>
        </div>
    </div>

    <!-- The container with the data of the editor. -->
    <div id="editor">
        <p>Hello world!</p>
    </div>
</div>

/* Give the editor some space and limits using a border. */
.ck-editor {
    margin: 1em 0;
    border: 1px solid hsla(0, 0%, 0%, 0.1);
    border-radius: 4px;
}

/* Adding internal spacing, border and background to the toolbar.  */
.ck-editor .btn-toolbar {
    padding: .5rem;
    background: hsl(240, 14%, 97%);
    border-bottom: 1px solid hsla(0, 0%, 0%, 0.1);
}

/* Tweaking the editable area for better readability. */
.ck-editor .ck-editor__editable {
    padding: 2em 2em 1em;
    overflow: auto;
}

/* When in read–only mode, the editable should fade out. */
.ck-editor .ck-editor__editable.ck-read-only {
    background: hsl(0, 0%, 98%);
    color: hsl(0, 0%, 47%);
}

/* Make sure the headings dropdown button does not change its size
as different headings are selected. */
.ck-editor .dropdown-toggle span {
    display: inline-block;
    width: 100px;
    text-align: left;
    overflow: hidden;
    text-overflow: ellipsis;
    vertical-align: bottom;
}

/* Make the headings dropdown items visually distinctive. */
.ck-editor .heading-item_heading1 { font-size: 1.5em; }
.ck-editor .heading-item_heading2 { font-size: 1.3em; }
.ck-editor .heading-item_heading3 { font-size: 1.1em; }

.ck-editor [class*="heading-item_"] {
    line-height: 22px;
    padding: 10px;
}

.ck-editor [class*="heading-item_heading"] {
  font-weight: bold;
}

/* Give the basic styles buttons the icon–like look and feel. */
.ck-editor #bold { font-weight: bold; }
.ck-editor #italic { font-style: italic; }
.ck-editor #underline { text-decoration: underline; }

this.ui = new BootstrapEditorUI( this );

// The class organizing the UI of the editor, binding it with existing Bootstrap elements in the DOM.
class BootstrapEditorUI extends EditorUI {
    constructor( editor ) {
        super( editor );

        // A helper to easily replace the editor#element with editor.editable#element.
        this._elementReplacer = new ElementReplacer();

        // The global UI view of the editor. It aggregates various Bootstrap DOM elements.
        const view = this._view = new EditorUIView( editor.locale );

        // This is the main editor element in the DOM.
        view.element = $( '.ck-editor' );

        // This is the editable view in the DOM. It will replace the data container in the DOM.
        view.editable = new InlineEditableUIView( editor.locale, editor.editing.view );

        // References to the dropdown elements for further usage. See #_setupBootstrapHeadingDropdown.
        view.dropdownMenu = view.element.find( '.dropdown-menu' );
        view.dropdownToggle = view.element.find( '.dropdown-toggle' );

        // References to the toolbar buttons for further usage. See #_setupBootstrapToolbarButtons.
        view.toolbarButtons = {};

        [ 'bold', 'italic', 'underline', 'undo', 'redo' ].forEach( name => {
            // Retrieve the jQuery object corresponding with the button in the DOM.
            view.toolbarButtons[ name ] = view.element.find( `#${ name }` );
        } );
    }

    // All EditorUI subclasses should expose their view instance
    // so other UI classes can access it if necessary.
    get view() {
        return this._view;
    }

    init( replacementElement ) {
        const editor = this.editor;
        const view = this.view;
        const editingView = editor.editing.view;

        // Make sure the EditorUIView is rendered. This will, for instance, create a place for UI elements
        // like floating panels detached from the main editor UI in DOM.
        this._view.render();

        // Create an editing root in the editing layer. It will correspond with the
        // document root created in the constructor().
        const editingRoot = editingView.document.getRoot();

        // The editable UI and editing root should share the same name.
        view.editable.name = editingRoot.rootName;

        // Render the editable component in the DOM first.
        view.editable.render();

        const editableElement = view.editable.element;

        // Register editable element so it is available via getEditableElement() method.
        this.setEditableElement( view.editable.name, editableElement );

        // Let the editable UI element respond to the changes in the global editor focus tracker
        // and let the focus tracker know about the editable element.
        this.focusTracker.add( editableElement );
        view.editable.bind( 'isFocused' ).to( this.focusTracker );

        // Bind the editable UI element to the editing view, making it an end– and entry–point
        // of the editor's engine. This is where the engine meets the UI.
        editingView.attachDomRoot( editableElement );

        // Setup the existing, external Bootstrap UI so it works with the rest of the editor.
        this._setupBootstrapToolbarButtons();
        this._setupBootstrapHeadingDropdown();

        // Replace the editor#element with editor.editable#element.
        this._elementReplacer.replace( replacementElement, editableElement );

        // Tell the world that the UI of the editor is ready to use.
        this.fire( 'ready' );
    }

    destroy() {
        // Restore the original editor#element.
        this._elementReplacer.restore();

        // Destroy the view.
        this._view.editable.destroy();
        this._view.destroy();

        super.destroy();
    }

    // This method activates Bold, Italic, Underline, Undo and Redo buttons in the toolbar.
    _setupBootstrapToolbarButtons() {
        ...
    }

    // This method activates the headings dropdown in the toolbar.
    _setupBootstrapHeadingDropdown() {
        ...
    }
}

editor.exectute( 'undo' );

const command = editor.commands.get( 'undo' );

command.on( 'change:isEnabled', ( evt, name, isEnabled ) => {
    if ( isEnabled ) {
        console.log( 'Whoa, you can undo some stuff now.' );
    } else {
        console.log( 'There is nothing to undo in the editor.' );
    }
} );

// This method activates Bold, Italic, Underline, Undo and Redo buttons in the toolbar.
_setupBootstrapToolbarButtons() {
    const editor = this.editor;

    for ( const name in this.view.toolbarButtons ) {
        // Retrieve the editor command corresponding with the ID of the button in the DOM.
        const command = editor.commands.get( name );
        const button = this.view.toolbarButtons[ name ];

        // Clicking the buttons should execute the editor command...
        button.click( () => editor.execute( name ) );

        // ...but it should not steal the focus so the editing is uninterrupted.
        button.mousedown( evt => evt.preventDefault() );

        const onValueChange = () => {
            button.toggleClass( 'active', command.value );
        };

        const onIsEnabledChange = () => {
            button.attr( 'disabled', () => !command.isEnabled );
        };

        // Commands can become disabled, e.g. when the editor is read-only.
        // Make sure the buttons reflect this state change.
        command.on( 'change:isEnabled', onIsEnabledChange );
        onIsEnabledChange();

        // Bold, Italic and Underline commands have a value that changes
        // when the selection starts in an element the command creates.
        // The button should indicate that e.g. you are editing text which is already bold.
        if ( !new Set( [ 'undo', 'redo' ] ).has( name ) ) {
            command.on( 'change:value', onValueChange );
            onValueChange();
        }
    }
}

// This method activates the headings dropdown in the toolbar.
_setupBootstrapHeadingDropdown() {
    const editor = this.editor;
    const dropdownMenu = this.view.dropdownMenu;
    const dropdownToggle = this.view.dropdownToggle;

    // Retrieve the editor commands for heading and paragraph.
    const headingCommand = editor.commands.get( 'heading' );
    const paragraphCommand = editor.commands.get( 'paragraph' );

    // Create a dropdown menu entry for each heading configuration option.
    editor.config.get( 'heading.options' ).map( option => {
        // Check if options is a paragraph or a heading as their commands differ slightly.
        const isParagraph = option.model === 'paragraph';

        // Create the menu item DOM element.
        const menuItem = $(
            `<a href="#" class="dropdown-item heading-item_${ option.model }">` +
                `${ option.title }` +
            '</a>'
        );

        // Upon click, the dropdown menu item should execute the command and focus
        // the editing view to keep the editing process uninterrupted.
        menuItem.click( () => {
            const commandName = isParagraph ? 'paragraph' : 'heading';
            const commandValue = isParagraph ? undefined : { value: option.model };

            editor.execute( commandName, commandValue );
            editor.editing.view.focus();
        } );

        dropdownMenu.append( menuItem );

        const command = isParagraph ? paragraphCommand : headingCommand;

        // Make sure the dropdown and its items reflect the state of the
        // currently active command.
        const onValueChange = isParagraph ? onValueChangeParagraph : onValueChangeHeading;
        command.on( 'change:value', onValueChange );
        onValueChange();

        // Heading commands can become disabled, e.g. when the editor is read-only.
        // Make sure the UI reflects this state change.
        command.on( 'change:isEnabled', onIsEnabledChange );

        onIsEnabledChange();

        function onValueChangeHeading() {
            const isActive = !isParagraph && command.value === option.model;

            if ( isActive ) {
                dropdownToggle.children( ':first' ).text( option.title );
            }

            menuItem.toggleClass( 'active', isActive );
        }

        function onValueChangeParagraph() {
            if ( command.value ) {
                dropdownToggle.children( ':first' ).text( option.title );
            }

            menuItem.toggleClass( 'active', command.value );
        }

        function onIsEnabledChange() {
            dropdownToggle.attr( 'disabled', () => !command.isEnabled );
        }
    } );
}

BootstrapEditor
    .create( $( '#editor' ).get( 0 ), {
        plugins: [
            Clipboard, Enter, Typing, Paragraph,
            BoldEditing, ItalicEditing, UnderlineEditing, HeadingEditing, UndoEditing
        ]
    } )
    .then( editor => {
        window.editor = editor;
    } )
    .catch( err => {
        console.error( err.stack );
    } );