debian-mirror-gitlab/doc/development/fe_guide/content_editor.md

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Content Editor development guidelines

The Content Editor is a UI component that provides a WYSIWYG editing experience for GitLab Flavored Markdown in the GitLab application. It also serves as the foundation for implementing Markdown-focused editors that target other engines, like static site generators.

We use Tiptap 2.0 and ProseMirror to build the Content Editor. These frameworks provide a level of abstraction on top of the native contenteditable web technology.

Usage guide

Follow these instructions to include the Content Editor in a feature.

1. Include the Content Editor component.
2. Set and get Markdown.
3. Listen for changes.

Include the Content Editor component

Import the ContentEditor Vue component. We recommend using asynchronous named imports to take advantage of caching, as the ContentEditor is a big dependency.

<script>
export default {
  components: {
    ContentEditor: () =>
      import(
        /* webpackChunkName: 'content_editor' */ '~/content_editor/components/content_editor.vue'
      ),
  },
  // rest of the component definition
}
</script>

The Content Editor requires two properties:

• renderMarkdown is an asynchronous function that returns the response (String) of invoking the Markdown API.
• uploadsPath is a URL that points to a GitLab upload service with multipart/form-data support.

See the WikiForm.vue component for a production example of these two properties.

Set and get Markdown

The ContentEditor Vue component doesn't implement Vue data binding flow (v-model) because setting and getting Markdown are expensive operations. Data binding would trigger these operations every time the user interacts with the component.

Instead, you should obtain an instance of the ContentEditor class by listening to the initialized event:

<script>
import { createAlert } from '~/alert';
import { __ } from '~/locale';

export default {
  methods: {
    async loadInitialContent(contentEditor) {
      this.contentEditor = contentEditor;

      try {
        await this.contentEditor.setSerializedContent(this.content);
      } catch (e) {
        createAlert({ message: __('Could not load initial document') });
      }
    },
    submitChanges() {
      const markdown = this.contentEditor.getSerializedContent();
    },
  },
};
</script>
<template>
  <content-editor
    :render-markdown="renderMarkdown"
    :uploads-path="pageInfo.uploadsPath"
    @initialized="loadInitialContent"
  />
</template>

Listen for changes

You can still react to changes in the Content Editor. Reacting to changes helps you know if the document is empty or dirty. Use the @change event handler for this purpose.

<script>
export default {
  data() {
    return {
      empty: false,
    };
  },
  methods: {
    handleContentEditorChange({ empty }) {
      this.empty = empty;
    }
  },
};
</script>
<template>
  <div>
    <content-editor
      :render-markdown="renderMarkdown"
      :uploads-path="pageInfo.uploadsPath"
      @initialized="loadInitialContent"
      @change="handleContentEditorChange"
    />
    <gl-button :disabled="empty" @click="submitChanges">
      {{ __('Submit changes') }}
    </gl-button>
  </div>
</template>

Implementation guide

The Content Editor is composed of three main layers:

• The editing tools UI, like the toolbar and the table structure editor. They display the editor's state and mutate it by dispatching commands.
• The Tiptap Editor object manages the editor's state, and exposes business logic as commands executed by the editing tools UI.
• The Markdown serializer transforms a Markdown source string into a ProseMirror document and vice versa.

Editing tools UI

The editing tools UI are Vue components that display the editor's state and dispatch commands to mutate it. They are located in the ~/content_editor/components directory. For example, the Bold toolbar button displays the editor's state by becoming active when the user selects bold text. This button also dispatches the toggleBold command to format text as bold:

sequenceDiagram
    participant A as Editing tools UI
    participant B as Tiptap object
    A->>B: queries state/dispatches commands
    B--)A: notifies state changes

Node views

We implement node views to provide inline editing tools for some content types, like tables and images. Node views allow separating the presentation of a content type from its model. Using a Vue component in the presentation layer enables sophisticated editing experiences in the Content Editor. Node views are located in ~/content_editor/components/wrappers.

Dispatch commands

You can inject the Tiptap Editor object to Vue components to dispatch commands.

NOTE: Do not implement logic that changes the editor's state in Vue components. Encapsulate this logic in commands, and dispatch the command from the component's methods.

<script>
export default {
  inject: ['tiptapEditor'],
  methods: {
    execute() {
      //Incorrect
      const { state, view } = this.tiptapEditor.state;
      const { tr, schema } = state;
      tr.addMark(state.selection.from, state.selection.to, null, null, schema.mark('bold'));

      // Correct
      this.tiptapEditor.chain().toggleBold().focus().run();
    },
  }
};
</script>
<template>

Query editor's state

Use the EditorStateObserver renderless component to react to changes in the editor's state, such as when the document or the selection changes. You can listen to the following events:

• docUpdate
• selectionUpdate
• transaction
• focus
• blur
• error.

Learn more about these events in the Tiptap event guide.

<script>
// Parts of the code has been hidden for efficiency
import EditorStateObserver from './editor_state_observer.vue';

export default {
  components: {
    EditorStateObserver,
  },
  data() {
    return {
      error: null,
    };
  },
  methods: {
    displayError({ message }) {
      this.error = message;
    },
    dismissError() {
      this.error = null;
    },
  },
};
</script>
<template>
  <editor-state-observer @error="displayError">
    <gl-alert v-if="error" class="gl-mb-6" variant="danger" @dismiss="dismissError">
      {{ error }}
    </gl-alert>
  </editor-state-observer>
</template>

The Tiptap editor object

The Tiptap Editor class manages the editor's state and encapsulates all the business logic that powers the Content Editor. The Content Editor constructs a new instance of this class and provides all the necessary extensions to support GitLab Flavored Markdown.

Implement new extensions

Extensions are the building blocks of the Content Editor. You can learn how to implement new ones by reading the Tiptap guide. We recommend checking the list of built-in nodes and marks before implementing a new extension from scratch.

Store the Content Editor extensions in the ~/content_editor/extensions directory. When using a Tiptap built-in extension, wrap it in a ES6 module inside this directory:

export { Bold as default } from '@tiptap/extension-bold';

Use the extend method to customize the Extension's behavior:

import { HardBreak } from '@tiptap/extension-hard-break';

export default HardBreak.extend({
  addKeyboardShortcuts() {
    return {
      'Shift-Enter': () => this.editor.commands.setHardBreak(),
    };
  },
});

Register extensions

Register the new extension in ~/content_editor/services/create_content_editor.js. Import the extension module and add it to the builtInContentEditorExtensions array:

import Emoji from '../extensions/emoji';

const builtInContentEditorExtensions = [
  Code,
  CodeBlockHighlight,
  Document,
  Dropcursor,
  Emoji,
  // Other extensions
]

The Markdown serializer

The Markdown Serializer transforms a Markdown String to a ProseMirror document and vice versa.

Deserialization

Deserialization is the process of converting Markdown to a ProseMirror document. We take advantage of ProseMirror's HTML parsing and serialization capabilities by first rendering the Markdown as HTML using the Markdown API endpoint:

sequenceDiagram
    participant A as Content Editor
    participant E as Tiptap Object
    participant B as Markdown Serializer
    participant C as Markdown API
    participant D as ProseMirror Parser
    A->>B: deserialize(markdown)
    B->>C: render(markdown)
    C-->>B: html
    B->>D: to document(html)
    D-->>A: document
    A->>E: setContent(document)

Deserializers live in the extension modules. Read Tiptap documentation about parseHTML and addAttributes to learn how to implement them. The Tiptap API is a wrapper around ProseMirror's schema spec API.

Serialization

Serialization is the process of converting a ProseMirror document to Markdown. The Content Editor uses prosemirror-markdown to serialize documents. We recommend reading the MarkdownSerializer and MarkdownSerializerState classes documentation before implementing a serializer:

sequenceDiagram
    participant A as Content Editor
    participant B as Markdown Serializer
    participant C as ProseMirror Markdown
    A->>B: serialize(document)
    B->>C: serialize(document, serializers)
    C-->>A: markdown string

prosemirror-markdown requires implementing a serializer function for each content type supported by the Content Editor. We implement serializers in ~/content_editor/services/markdown_serializer.js.