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guideDefining a model and a view

This guide will show you how to create a simple abbreviation plugin for CKEditor 5.

We will create a toolbar button that lets the users insert abbreviations into their document. These abbreviations will use the <abbr> HTML element with a ‘title’ attribute that will show up in a tooltip when the user hovers over the element. You can check the mechanism hovering over the underlined “HTML” text in the previous sentence.

This first part of the tutorial will cover the basics. We will just insert one possible abbreviation: “WYSIWYG.” We will get user input in the next part of this tutorial series.

If you want to see the final product of this tutorial before you plunge in, check out the live demo.

# Let’s start!

The easiest way to set up your project is to grab the starter files from the GitHub repository for this tutorial. We gathered all the necessary dependencies there, including some CKEditor 5 packages and other files needed to build the editor.

The editor has already been created in the app.js file with some basic plugins. All you need to do is clone the repository, navigate to the starter-files directory, run the npm install command, and you can start coding right away.

The webpack is also already configured, so you can just use the npm run build command to build your application. Whenever you want to check anything in the browser, save the changes and run build again. Then, refresh the page in your browser (remember to turn off caching, so that new changes are displayed instantly).

The starter files come with the CKEditor 5 Inspector attached to the editor, so you can debug and observe what is happening in the model and the view layers. It will give you tons of useful information about the state of the editor such as internal data structures, selection, commands, and many more.

If you want to set up the project yourself, you should follow the steps listed in the the “Quick start” section. Additionally, you will need to install the @ckeditor/ckeditor5-core package, which contains the Plugin class, and the @ckeditor/ckeditor5-ui package, which contains the UI library and the framework.

Your entry point to the plugin is app.js:

// app.js

import { ClassicEditor } from '@ckeditor/ckeditor5-editor-classic';
import { Bold, Italic } from '@ckeditor/ckeditor5-basic-styles';
import { Essentials } from '@ckeditor/ckeditor5-essentials';
import { Heading } from '@ckeditor/ckeditor5-heading';
import { List } from '@ckeditor/ckeditor5-list';
import { Paragraph } from '@ckeditor/ckeditor5-paragraph';

ClassicEditor
    .create( document.querySelector( '#editor' ), {
        plugins: [ Essentials, Paragraph, Heading, List, Bold, Italic ],
        toolbar: [ 'heading', 'bold', 'italic', 'numberedList', 'bulletedList' ]
    } )
    .then( editor => {
        console.log( 'Editor was initialized', editor );
        CKEditorInspector.attach( editor );
    } )
    .catch( error => {
        console.error( error.stack );
    } );

Now take look at index.html. We added the <abbr> element. It will not work just yet, but we will fix that in a couple of steps.

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <title>CKEditor 5 Framework – Abbreviation plugin</title>
    </head>
    <body>
        <div id="editor">
 			<h2>Abbreviation plugin</h2>
            <p>CKEditor5 is a modern, feature-rich, world-class <abbr title="What You See Is What You Get">WYSIWYG</abbr> editor.</p>
        </div>

        <script src="dist/bundle.js"></script>
    </body>
</html>

# Plugin structure

Our abbreviation plugin is divided into three components – Abbreviation, AbbreviationUI, and AbbreviationEditing:

  • AbbreviationEditing will enable the abbreviation attribute in the model and introduce a proper model ←→ view conversion.
  • AbbreviationUI will be responsible for the UI – the toolbar button.
  • Abbreviation will be the glue that holds the UI and the editing together.

We put them in the /abbreviation directory. We will be adding more files the in the next parts of the tutorial. This is our directory structure:

├── app.js
├── dist
│   ├── bundle.js
│   └── bundle.js.map
├── index.html
├── node_modules
├── package.json
├── abbreviation
│   ├── abbreviation.js
│   ├── abbreviationediting.js
│   └── abbreviationui.js
└── webpack.config.js

Take a look at the 3 components, which have already been defined and imported into app.js.

AbbreviationUI:

// abbreviation/abbreviationui.js

import { Plugin } from '@ckeditor/ckeditor5-core';

export default class AbbreviationUI extends Plugin {
    init() {
        console.log( 'AbbreviationUI#init() got called' );
    }
}

AbbreviationEditing:

// abbreviation/abbreviationediting.js

import { Plugin } from '@ckeditor/ckeditor5-core';

export default class AbbreviationEditing extends Plugin {
    init() {
        console.log( 'AbbreviationEditing#init() got called' );
    }
}

Abbreviation:

// abbreviation/abbreviation.js

import AbbreviationEditing from './abbreviationediting';
import AbbreviationUI from './abbreviationui';
import { Plugin } from '@ckeditor/ckeditor5-core';

export default class Abbreviation extends Plugin {
    static get requires() {
        return [ AbbreviationEditing, AbbreviationUI ];
    }
}

Now we need to load the Abbreviation plugin in our app.js file. The editor will load the AbbreviationUI and the AbbreviationEditing components by itself, as they are required by our “glue” plugin.

// app.js

import { ClassicEditor } from '@ckeditor/ckeditor5-editor-classic';
import { Bold, Italic } from '@ckeditor/ckeditor5-basic-styles';
import { Essentials } from '@ckeditor/ckeditor5-essentials';
import { Heading } from '@ckeditor/ckeditor5-heading';
import { List } from '@ckeditor/ckeditor5-list';
import { Paragraph } from '@ckeditor/ckeditor5-paragraph';

import CKEditorInspector from '@ckeditor/ckeditor5-inspector';

import Abbreviation from './abbreviation/abbreviation';					// ADDED

ClassicEditor
    .create( document.querySelector( '#editor' ), {
        plugins: [
            Essentials, Paragraph, Heading, List, Bold, Italic,
            Abbreviation												// ADDED
        ],
        toolbar: [ 'heading', 'bold', 'italic', 'numberedList', 'bulletedList' ]
    } )
    .then( editor => {
        console.log( 'Editor was initialized', editor );
    } )
    .catch( error => {
        console.error( error.stack );
    } );

Rebuild the project now, refresh the browser and you should see that the AbbreviationEditing and AbbreviationUI plugins were loaded.

# The model and the view layers

CKEditor 5 implements its own custom data model, which does not map 1:1 to the DOM. The model document is converted into the view, which represents the content that the user is editing.

Before moving forward, it is important to understand the editor architecture. Read more about the model and the view to get familiar with the basic concepts.

In the view layer, we will have the <abbr> HTML element, with a title attribute. See how it will look like in the inspector.
Screenshot of a the inspector showing the view layer.

In the model, inline elements such as <abbr>, are represented as attributes not as separate elements. In order for our plugin to work, we will need to make sure that we can add abbreviation attribute to the text node.
Screenshot of a the inspector showing the model layer.

# Defining the schema

We can do it by defining the model’s schema. Thanks to a couple lines of code, we will allow all text nodes to receive the model abbreviation attribute.

Schema defines what is allowed in the model in terms of structures, attributes, and other characteristics. This information is then used by the features and the engine to make decisions on how to process the model, so it is crucial that your custom plugins have a well-defined schema. Read more about it in our introduction to the editing engine architecture.

We will just extend the text node’s schema to accept our abbreviation attribute, using the schema.extend() method.

Update the AbbreviationEditing plugin with this definition:

// abbreviation/abbreviationediting.js

import { Plugin } from '@ckeditor/ckeditor5-core';

export default class AbbreviationEditing extends Plugin {
    init() {
        this._defineSchema();									// ADDED
    }

    _defineSchema() {											// ADDED
        const schema = this.editor.model.schema;

        // Extend the text node's schema to accept the abbreviation attribute.
        schema.extend( '$text', {
            allowAttributes: [ 'abbreviation' ]
        } );
    }
}

# Defining converters

Converters tell the editor how to transform the view to the model (for example, when loading the data to the editor or handling pasted content) and how to render the model to the view (for editing purposes, or when retrieving the editor data).

Conversion is one of the more complex topics in our editing engine architecture. It is definitely worth reading more about the conversion in the editor before you move on.

We will need to convert the model abbreviation attribute into a view element (downcast) and vice versa (upcast). We can achieve this by using our conversion helpers and defining what the model and the view is supposed to look like for both conversions.

Converting the full title of the abbreviation is a little bit tricky, because we need to make sure that its value is synchronized between the model and the view.

# Downcast conversion

In the downcast conversion, we will use one of our conversion helpers – attributeToElement() – to transform the model abbreviation attribute into the view <abbr> element.

We will need to use a callback function to get the title stored as a model attribute value and transform it into the title value of the view element. Here, the second parameter of the view callback is the DowncastConversionApi object. We will use its writer property, which will allow us to manipulate the data during downcast conversion, as it contains an instance of the DowncastWriter.

// abbreviation/abbreviationediting.js

import { Plugin } from '@ckeditor/ckeditor5-core';

export default class AbbreviationEditing extends Plugin {
    init() {
        this._defineSchema();
        this._defineConverters();							// ADDED
    }

    _defineSchema() {
    // Previously defined schema.
    // ...
    }

    _defineConverters() {									// ADDED
        const conversion = this.editor.conversion;

        // Conversion from a model attribute to a view element.
        conversion.for( 'downcast' ).attributeToElement( {
            model: 'abbreviation',
            // Callback function provides access to the model attribute value
            // and the DowncastWriter.
            view: ( modelAttributeValue, conversionApi ) => {
                const { writer } = conversionApi;

                return writer.createAttributeElement( 'abbr', {
                    title: modelAttributeValue
                } );
            }
        } );

    }
}

# Upcast conversion

The upcast conversion tells the editor how the view <abbr> element is supposed to look like in the model. We will transform it using another conversion helper – elementToAttribute().

We also need to grab the title value from the content and use it in the model. We can do that thanks to a callback function, which gives us the access to the view element.

// abbreviation/abbreviationediting.js

import { Plugin } from '@ckeditor/ckeditor5-core';

export default class AbbreviationEditing extends Plugin {
    init() {
    // Schema and converters initialization.
    // ...
    }

    _defineSchema() {
    // Previously defined schema.
    // ...
    }

    _defineConverters() {
        const conversion = this.editor.conversion;

        conversion.for( 'downcast' ).attributeToElement(
        // Code responsible for downcast conversion.
        // ...
        );

        // Conversion from a view element to a model attribute.
        conversion.for( 'upcast' ).elementToAttribute( {
            view: {
                name: 'abbr',
                attributes: [ 'title' ]
            },
            model: {
                key: 'abbreviation',
                // Callback function provides access to the view element.
                value: viewElement => {
                    const title = viewElement.getAttribute( 'title' );

                    return title;
                }
            }
        } );
    }
}

Thanks to the upcast conversion, our abbreviation added in the index.html should work now. Rebuild the editor and check it out yourself.

Screenshot of the editor showing working abbreviation.

# Creating a toolbar button

Now we can create our Abbreviation toolbar button using the ButtonView class.

We need to register it in the editor’s UI componentFactory, so it can be displayed in the toolbar.

// abbreviation/abbreviationui.js

import { Plugin } from '@ckeditor/ckeditor5-core';
import { ButtonView } from '@ckeditor/ckeditor5-ui';

export default class AbbreviationUI extends Plugin {
    init() {
        const editor = this.editor;

        editor.ui.componentFactory.add( 'abbreviation', () => {
            const button = new ButtonView();

            button.label = 'Abbreviation';
            button.tooltip = true;
            button.withText = true;

            return button;
        } );
    }
}

We passed the name of the button in the componentFactory.add, so it is now available to use in the toolbar configuration. We can now simply add it to the toolbar in app.js:

// app.js

import { ClassicEditor } from '@ckeditor/ckeditor5-editor-classic';
import { Bold, Italic } from '@ckeditor/ckeditor5-basic-styles';
import { Essentials } from '@ckeditor/ckeditor5-essentials';
import { Heading } from '@ckeditor/ckeditor5-heading';
import { List } from '@ckeditor/ckeditor5-list';
import { Paragraph } from '@ckeditor/ckeditor5-paragraph';

import Abbreviation from './abbreviation/abbreviation';

ClassicEditor
    .create( document.querySelector( '#editor' ), {
        plugins: [
            Essentials, Paragraph, Heading, List, Bold, Italic, Abbreviation
        ],
        toolbar: [
            'heading', 'bold', 'italic', 'numberedList', 'bulletedList', '|',
            'abbreviation'												  // ADDED
        ]
    } )
    .then( editor => {
        console.log( 'Editor was initialized', editor );
    } )
    .catch( error => {
        console.error( error.stack );
    } );

We have the button, so let’s define what should happen after the user clicks it.

We will use the insertContent() method to insert our abbreviation and its title attribute into the document. Inside, we just need to create a new text node with writer.createText().

// abbreviation/abbreviationui.js

import { Plugin } from '@ckeditor/ckeditor5-core';
import { ButtonView } from '@ckeditor/ckeditor5-ui';

export default class AbbreviationUI extends Plugin {
    init() {
        const editor = this.editor;

        editor.ui.componentFactory.add( 'abbreviation', () => {
            // Previously initialized button view.
            // ...

            this.listenTo( button, 'execute', () => {
                const selection = editor.model.document.selection;
                const title = 'What You See Is What You Get';
                const abbr = 'WYSIWYG';

                // Change the model to insert the abbreviation.
                editor.model.change( writer => {
                    editor.model.insertContent(
                        // Create a text node with the abbreviation attribute.
                        writer.createText( abbr, { abbreviation: title } )
                    );
                } );
            } );

            return button;
        } );
    }
}

# Demo

Abbreviation plugin

CKEditor 5 is a modern, feature-rich, world-class WYSIWYG editor.

# Final code

If you got lost at any point, this is the final implementation of the plugin. You can paste the code from different files into your project, or clone and install the whole thing, and it will run out-of-the-box.

What’s next

That’s it for the first part of this tutorial! Your plugin should now work (at least in its most basic form). Move on to the second part, where you will create a balloon with a form to get user’s input, replacing our hard-coded “WYSIWYG” abbreviation.