1.0.0 • Public • Published


Simple no-frills code editor with syntax highlighting.


Several browser based code editors such as Ace, CodeMirror, Monaco etc. provide the ability to embed a full-featured code editor in your web page. However, if you just need a simple editor with syntax highlighting without any of the extra features, they can be overkill as they don't usually have a small bundle size footprint. This library aims to provide a simple code editor with syntax highlighting support without any of the extra features, perfect for simple embeds and forms where users can submit code.


  • Syntax highlighting with third party library
  • Tab key support with customizable indentation
  • Automatic indent on new lines
  • Undo whole words instead of letter by letter
  • Read only property
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npm install react-code-viewer


You need to use the editor with a third party library which provides syntax highlighting. For example, it'll look like following with prismjs:

import React from 'react';
import Viewer from 'react-code-viewer';
import { highlight, languages } from 'prismjs/components/prism-core';
import 'prismjs/components/prism-clike';
import 'prismjs/components/prism-javascript';
const code = `function add(a, b) {
  return a + b;
class App extends React.Component {
  state = { code };
  render() {
    return (
        onValueChange={code => this.setState({ code })}
        highlight={code => highlight(code, languages.js)}
          fontFamily: '"Fira code", "Fira Mono", monospace',
          fontSize: 12,


  • value (string): Current value of the editor. Pass the code to display as a prop.
  • onValueChange (string => mixed): Callback which is called when the value of the editor changes. You'll need to update the value prop when this is called.
  • highlight (string => string): Callback which will receive text to highlight. You'll need to return HTML with syntax highlighting using a library such as prismjs.
  • tabSize (number): Optional prop to control the tab size. For example, for 4 space indentation, tabSize will be 4 and insertSpaces will be true. Default: 2.
  • insertSpaces (boolean): Optional prop to control whether to use spaces for indentation. Default: true.
  • padding (number): Optional padding for code. Default: 0.
  • readOnly (boolean): Optional read only property for code. Default: false.


How it works

It works by overlaying a syntax highlighted <pre> block over a <textarea>. When you type, select, copy text etc., you interact with the underlying <textarea>, so the experience feels native. This is a very simple approach compared to other editors which re-implement the behaviour.

The syntax highlighting can be done by any third party library as long as it returns HTML and is fully controllable by the user.

The vanilla <textarea> doesn't support inserting tab characters for indentation, so we re-implement it by listening to keydown events and programmatically updating the text. One caveat with programmatically updating the text is that we lose the undo stack, so we need to maintain our own undo stack. As a result, we can also implement improved undo behaviour such as undoing whole words similar to editors like VSCode.

Known issues

Using the undo/redo option from browser's context menu can mess things up.


While developing, you can run the example app to test your changes:

yarn example

Make sure your code passes Flow and ESLint. Run the following to verify:

yarn flow
yarn lint

To fix formatting errors, run the following:

yarn lint -- --fix


npm i react-code-viewer

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  • rjoydip