Source Editor

Source Editor provides the editing experience at GitLab. This thin wrapper around the Monaco editor provides necessary helpers and abstractions, and extends Monaco using extensions. Multiple GitLab features use it, including:

When to use Source Editor

Use Source Editor only when users need to edit the file content. If you only need to display source code, consider using the BlobContent component.

If the page you’re working on is already loading the Source Editor, displaying read-only content in the Source Editor is still a valid option.

How to use Source Editor

Source Editor is framework-agnostic and can be used in any application, including both Rails and Vue. To help with integration, we have the dedicated <source-editor> Vue component, but the integration of Source Editor is generally straightforward:

  1. Import Source Editor:

    import SourceEditor from '~/editor/source_editor';
  2. Initialize global editor for the view:

    const editor = new SourceEditor({
      // Editor Options.
      // The list of all accepted options can be found at
  3. Create an editor’s instance:

      // Source Editor configuration options.

An instance of Source Editor accepts the following configuration options:

Option Required? Description
el true HTML Node: The element on which to render the editor.
blobPath false String: The name of a file to render in the editor, used to identify the correct syntax highlighter to use with that file, or another file type. Can accept wildcards like *.js when the actual filename isn’t known or doesn’t play any role.
blobContent false String: The initial content to render in the editor.
extensions false Array: Extensions to use in this instance.
blobGlobalId false String: An auto-generated property.
Note: This property may go away in the future. Do not pass blobGlobalId unless you know what you’re doing.
Editor Options false Object(s): Any property outside of the list above is treated as an Editor Option for this particular instance. Use this field to override global Editor Options on the instance level. A full index of Editor Options is available.


The editor uses the same public API as provided by Monaco editor with additional functions on the instance level:

Function Arguments Description
updateModelLanguage path: String Updates the instance’s syntax highlighting to follow the extension of the passed path. Available only on the instance level.
use Array of objects Array of extensions to apply to the instance. Accepts only an array of objects. The extensions’ ES6 modules must be fetched and resolved in your views or components before they’re passed to use. Available on the instance and global editor (all instances) levels.
Monaco Editor options See documentation Default Monaco editor options.


  1. Editor’s loading state.

    The loading state is built in to Source Editor, making spinners and loaders rarely needed in HTML. To benefit the built-in loading state, set the data-editor-loading property on the HTML element that should contain the editor. When bootstrapping, Source Editor shows the loader automatically.

    Source Editor: loading state

  2. Update syntax highlighting if the filename changes.

    // fileNameEl here is the HTML input element that contains the filename
    fileNameEl.addEventListener('change', () => {
  3. Get the editor’s content.

    We may set up listeners on the editor for every change, but it rapidly can become an expensive operation. Instead, get the editor’s content when it’s needed. For example, on a form’s submission:

    form.addEventListener('submit', () => {
      my_content_variable = this.editor.getValue();
  4. Performance

    Even though Source Editor itself is extremely slim, it still depends on Monaco editor, which adds weight. Every time you add Source Editor to a view, the JavaScript bundle’s size significantly increases, affecting your view’s loading performance. We recommend you import the editor on demand if either:

    • You’re uncertain if the view needs the editor.
    • The editor is a secondary element of the view.

    Loading Source Editor on demand is handled like loading any other module:

    someActionFunction() {
      import(/* webpackChunkName: 'SourceEditor' */ '~/editor/source_editor').
        then(({ default: SourceEditor }) => {
          const editor = new SourceEditor();


Source Editor provides a universal, extensible editing tool to the whole product, and doesn’t depend on any particular group. Even though the Source Editor’s core is owned by Create::Editor FE Team, any group can own the extensions—the main functional elements. The goal of Source Editor extensions is to keep the editor’s core slim and stable. Any needed features can be added as extensions to this core. Any group can build and own new editing features without worrying about changes to Source Editor breaking or overriding them.

You can depend on other modules in your extensions. This organization helps keep the size of Source Editor’s core at bay by importing dependencies only when needed.

Structurally, the complete implementation of Source Editor can be presented as this diagram:

%%{init: { "fontFamily": "GitLab Sans" }}%% graph TD; B[Extension 1]---A[Source Editor] C[Extension 2]---A[Source Editor] D[Extension 3]---A[Source Editor] E[...]---A[Source Editor] F[Extension N]---A[Source Editor] A[Source Editor]---Z[Monaco]

An extension is an ES6 module that exports a JavaScript object:

import { Position } from 'monaco-editor';

export default {
  navigateFileStart() {
    this.setPosition(new Position(1, 1));

In the extension’s functions, this refers to the current Source Editor instance. Using this, you get access to the complete instance’s API, such as the setPosition() method in this particular case.

Using an existing extension

Adding an extension to Source Editor’s instance requires the following steps:

import SourceEditor from '~/editor/source_editor';
import MyExtension from '~/my_extension';

const editor = new SourceEditor().createInstance({

Creating an extension

Let’s create our first Source Editor extension. Extensions are ES6 modules exporting a basic Object, used to extend Source Editor’s features. As a test, let’s create an extension that extends Source Editor with a new function that, when called, outputs the editor’s content in alert.


export default {
  throwContentAtMe() {

In the code example, this refers to the instance. By referring to the instance, we can access the complete underlying Monaco editor API, which includes functions like getValue().

Now let’s use our extension:


import SourceEditor from '~/editor/source_editor';
import MyFancyExtension from './my_fancy_extension';

const editor = new SourceEditor().createInstance({
someButton.addEventListener('click', () => {

First of all, we import Source Editor and our new extension. Then we create the editor and its instance. By default Source Editor has no throwContentAtMe method. But the editor.use(MyFancyExtension) line brings that method to our instance. After that, we can use it any time we need it. In this case, we call it when some theoretical button has been clicked.

This script would result in an alert containing the editor’s content when someButton is clicked.

Source Editor new extension's result


  1. Performance

    Just like Source Editor itself, any extension can be loaded on demand to not harm loading performance of the views:

    const EditorPromise = import(
      /* webpackChunkName: 'SourceEditor' */ '~/editor/source_editor'
    const MarkdownExtensionPromise = import('~/editor/source_editor_markdown_ext');
    Promise.all([EditorPromise, MarkdownExtensionPromise])
      .then(([{ default: SourceEditor }, { default: MarkdownExtension }]) => {
        const editor = new SourceEditor().createInstance({
  2. Using multiple extensions

    Just pass the array of extensions to your use method:

    editor.use([FileTemplateExtension, MyFancyExtension]);