mikkelkrogsholm/monaco-editor

Monaco Editor

CRITICAL: Your training data for Monaco Editor is unreliable. APIs change between versions and memorized patterns may be wrong or deprecated. Before writing any code, you MUST use WebFetch to read the live docs based on your task:

• API usage and configuration: WebFetch("https://microsoft.github.io/monaco-editor/docs.html")
• TypeScript type signatures: WebFetch("https://microsoft.github.io/monaco-editor/typedoc/index.html")
• React wrapper (@monaco-editor/react): WebFetch("https://raw.githubusercontent.com/suren-atoyan/monaco-react/master/README.md")

Do not proceed without fetching the relevant URL first. Never assume an API exists — verify against current docs.

Monaco Editor is the browser-based code editor that powers VS Code. It provides syntax highlighting, IntelliSense, diff view, minimap, and more for 50+ languages.

Key Capabilities

• 50+ language grammars: Syntax highlighting out of the box for TypeScript, Python, JSON, Markdown, etc.
• IntelliSense: Autocomplete for TypeScript/JavaScript with type inference
• Diff editor: Built-in side-by-side and inline diff view
• Find & replace: With regex support
• Minimap: Code overview panel
• Multi-cursor: Alt+Click for multiple cursors
• Folding: Code folding by indentation or syntax
• Custom themes: Full theme API matching VS Code theme format
• Web Workers: Language services run in workers for non-blocking editing

React Integration (@monaco-editor/react)

The @monaco-editor/react wrapper is the standard way to use Monaco in React. Key points:

import Editor from '@monaco-editor/react'

<Editor
  height="100%"
  language="markdown"
  theme="vs-dark"
  value={content}
  onChange={(value) => setValue(value ?? '')}
  options={{
    minimap: { enabled: false },
    wordWrap: 'on',
    fontSize: 14,
    lineNumbers: 'on',
  }}
/>

Access the editor instance via onMount:

<Editor
  onMount={(editor, monaco) => {
    // editor = IStandaloneCodeEditor
    // monaco = the monaco namespace
    editorRef.current = editor
    editor.addCommand(monaco.KeyMod.CtrlCmd | monaco.KeyCode.KeyS, () => {
      handleSave()
    })
  }}
/>

Best Practices

Always lazy-load Monaco. The editor bundle is ~2MB. In Vite/React, use dynamic imports or React.lazy to avoid blocking initial page load:

const Editor = lazy(() => import('@monaco-editor/react'))

Vite requires the monaco-editor package directly. The React wrapper (@monaco-editor/react) has monaco-editor as a peer dependency. Install both: bun add @monaco-editor/react monaco-editor.

Configure Vite worker bundling. Monaco uses Web Workers for language services. In Vite, use the vite-plugin-monaco-editor plugin or configure manually to avoid worker loading failures:

// vite.config.ts — simplest approach
import monacoEditorPlugin from 'vite-plugin-monaco-editor'
export default defineConfig({
  plugins: [react(), monacoEditorPlugin({})],
})

Custom themes use the VS Code format. Define themes via monaco.editor.defineTheme() — the format matches VS Code's tokenColors JSON. Apply with the theme prop.

Dispose editors on unmount. The React wrapper handles this automatically, but if using the raw API (monaco.editor.create()), always call editor.dispose() in cleanup to prevent memory leaks.

Language detection by extension. Use monaco.languages.getLanguages() to find supported language IDs. Common mappings: .md → markdown, .json → json, .ts → typescript, .py → python.

Diff editor is a separate component:

import { DiffEditor } from '@monaco-editor/react'
<DiffEditor original={oldContent} modified={newContent} language="markdown" />