Fancy-ANSI is a small JavaScript library for converting ANSI to beautiful, browser-safe HTML

Demo: https://www.kubetail.com/demo
Preview: https://kubetail-org.github.io/fancy-ansi/

While adding ANSI markup support to kubetail we tested out several popular popular ANSI-to-html conversion libraries (e.g. ansi-html-community, ansi-to-html, ansi_up) and ran into a few problems:

• Failure to parse some of our users' ANSI markup
• Use of hard-coded styles that made customization more difficult
• Lack of support for CSS variables

To solve these problems and make something that integrated nicely into our frontend stack (Tailwind, React) we created Fancy-ANSI. The library is designed to be small (~4 kb gzipped), performant, easy-to-use and safe from XSS attacks. It has the following features:

• Supports easy customization using CSS variables
• Supports almost all SGR codes
• Includes a Tailwind plugin that enables support for easy theming
• Includes a React component for easy use in a React environment
• Includes useful utilities like hasAnsi() and stripAnsi() that come in handy when working with ANSI
• Includes popular color palettes that can be swapped in easily

Try it out and let us know what you think! If you notice any bugs or have any feature requests just create a GitHub Issue.

Install the library using your favorite package manager:

# npm
npm install fancy-ansi

# yarn
yarn add fancy-ansi

# pnpm
pnpm add fancy-ansi

Now you can use it in your code with React:

// ExampleComponent.jsx
import { AnsiHtml } from 'fancy-ansi/react';

export const ExampleComponent = () => {
  const text = '\x1b[34mhello \x1b[33mworld\x1b[0m';
  return <AnsiHtml className="font-mono whitespace-pre text-sm" text={text} />;
};

Or with Vanilla-JS:

// example.ts
import { FancyAnsi } from 'fancy-ansi';

const fancyAnsi = new FancyAnsi();

export function addElementWithAnsi() {
  const el = document.createElement('div');
  el.innerHTML = fancyAnsi.toHtml('\x1b[34mhello \x1b[33mworld\x1b[0m');
  document.body.append(el);
}

The HTML rendered is browser-safe and ready with some sensible color choices that can be customized easily (see below).

You can configure Fancy-ANSI using CSS variables. For example, to invert blacks in dark mode you can change the value of black when the document has a "dark" class:

:root {
  --ansi-black: #000;
}

.dark {
  --ansi-black: #FFF;
}

The full list of supported variables can be found in the SGR Parameters section below.

Extended colors:

The Fancy-ANSI Tailwind plugin makes it easy to support theming and to access multiple built-in palettes from your css. To use the plugin, add it to your tailwind.config.js file:

// tailwind.config.js
module.exports = {
  plugins: [
    // ...
    require('fancy-ansi/plugin')
  ]
}

Now you can access the built-in palettes using the Tailwind theme() function. For example, you can implement two different palettes for light/dark mode like this:

/* index.css */
@tailwind base;
@tailwind components;
@tailwind utilities;

@layer base {
  :root {
    --ansi-black: theme(ansi.colors.vscode.black);
    --ansi-red: theme(ansi.colors.vscode.red);
    --ansi-green: theme(ansi.colors.vscode.green);
    --ansi-yellow: theme(ansi.colors.vscode.yellow);
    --ansi-blue: theme(ansi.colors.vscode.blue);
    --ansi-magenta: theme(ansi.colors.vscode.magenta);
    --ansi-cyan: theme(ansi.colors.vscode.cyan);
    --ansi-white: theme(ansi.colors.vscode.white);
    --ansi-bright-black: theme(ansi.colors.vscode.bright-black);
    --ansi-bright-red: theme(ansi.colors.vscode.bright-red);
    --ansi-bright-green: theme(ansi.colors.vscode.bright-green);
    --ansi-bright-yellow: theme(ansi.colors.vscode.bright-yellow);
    --ansi-bright-blue: theme(ansi.colors.vscode.bright-blue);
    --ansi-bright-magenta: theme(ansi.colors.vscode.magenta);
    --ansi-bright-cyan: theme(ansi.colors.vscode.cyan);
    --ansi-bright-white: theme(ansi.colors.vscode.white);
  }

  .dark {
    --ansi-black: theme(ansi.colors.xtermjs.black);
    --ansi-red: theme(ansi.colors.xtermjs.red);
    --ansi-green: theme(ansi.colors.xtermjs.green);
    --ansi-yellow: theme(ansi.colors.xtermjs.yellow);
    --ansi-blue: theme(ansi.colors.xtermjs.blue);
    --ansi-magenta: theme(ansi.colors.xtermjs.magenta);
    --ansi-cyan: theme(ansi.colors.xtermjs.cyan);
    --ansi-white: theme(ansi.colors.xtermjs.white);
    --ansi-bright-black: theme(ansi.colors.xtermjs.bright-black);
    --ansi-bright-red: theme(ansi.colors.xtermjs.bright-red);
    --ansi-bright-green: theme(ansi.colors.xtermjs.bright-green);
    --ansi-bright-yellow: theme(ansi.colors.xtermjs.bright-yellow);
    --ansi-bright-blue: theme(ansi.colors.xtermjs.bright-blue);
    --ansi-bright-magenta: theme(ansi.colors.xtermjs.magenta);
    --ansi-bright-cyan: theme(ansi.colors.xtermjs.cyan);
    --ansi-bright-white: theme(ansi.colors.xtermjs.white);
  }

Fancy-ANSI has a convenient React component that you can import from the fancy-ansi/react module:

// ExampleComponent.jsx
import { AnsiHtml } from 'fancy-ansi/react';

export const ExampleComponent = () => {
  const text = '\x1b[34mhello \x1b[33mworld\x1b[0m';
  return <AnsiHtml className="font-mono whitespace-pre text-sm" text={text} />;
};

You can see some example implementations in the examples/ directory:

• Vite - React
• Next.js

FancyAnsi

  toHtml(input)
    * @param {string} input - The input string
    * @returns {string} Browser-safe HTML string containing stylized ANSI content

Example:

  import { FancyAnsi } from 'fancy-ansi';

  const fancyAnsi = new FancyAnsi();
  fancyAnsi.toHtml('\x1b[1mThis is in bold.\x1b[0m');

hasAnsi(input)

  * @param {string} input - The input string
  * @returns {boolean} Boolean indicating whether or not input string contains ANSI markup

Example:

  import { hasAnsi } from 'fancy-ansi';

  if (hasAnsi('\x1b[1mThis is in bold.\x1b[0m')) {
    console.log('string has ansi');
  } else {
    console.log('string doesn\'t have ansi');
  }

stripAnsi(input)

  * @param {string} input - The input string
  * @returns {string} Content of input string with ANSI markup removed

Example:

  import { stripAnsi } from 'fancy-ansi';

  const withoutAnsi = stripAnsi('\x1b[1mThis is in bold.\x1b[0m');
  console.log(`string without ansi: ${withoutAnsi}`);

`fancy-ansi/colors` module

Example:

  import { xtermjs, terminalapp } from 'fancy-ansi/colors';

  console.log(`xterm.js red: ${xtermjs.red}`);
  console.log(`Terminal.app red: ${terminalapp.red}`);

Available palettes:

  * eclipse
  * putty
  * terminalapp
  * ubuntu
  * vga
  * vscode
  * windows10
  * xterm
  * xtermjs

To develop Fancy-ANSI, first clone the repository then install the dependencies:

git clone git@github.com:kubetail-org/fancy-ansi.git
cd fancy-ansi
pnpm install

Fancy-ANSI uses vite for development. To run run the vite dev server, use the dev command:

pnpm dev

Now you can access the demo page and see your changes at http://localhost:5173/.

Fancy-ANSI uses jest for testing (via vitest). To run the tests, use the test command:

pnpm test

The test files are colocated with the source code in the src/ directory, with the filename format {name}.test.(ts|tsx).

To build Fancy-ANSI for production, run the build command:

pnpm build

The production files will be located in the dist/ directory.

• The ANSI parsing code is from ansi_up
• has/strip methods use Chalk's ansi-regex
• Fancy Nancy