Syntax Highlighting and Code Editing in React: A Technical Deep Dive

A lean Prism highlighter component for React

Comes with everything to render Prismjs syntax highlighted code directly in React & React Native!

Introduction

Prism React Renderer powers syntax highlighting in the amazing Docusaurus framework and many others.

This library tokenises code using Prism and provides a small render-props-driven component to quickly render it out into React. This is why it even works with React Native! It's bundled with a modified version of Prism that won't pollute the global namespace and comes with a couple of common language syntaxes.

(There's also an escape-hatch to use your own Prism setup, just in case)

It also comes with its own VSCode-like theming format, which means by default you can easily drop in different themes, use the ones this library ships with, or create new ones programmatically on the fly.

(If you just want to use your Prism CSS-file themes, that's also no problem)

Table of Contents

• Installation
  • Usage
  • Custom Language Support
• Basic Props
  • children
  • language
  • code
• Advanced Props
  • theme
  • prism
• Children Function
  • state
  • prop getters
    • getLineProps
    • getTokenProps
• Utility Functions
  • normalizeTokens
  • useTokenize
• Theming
• Upgrading from v1 to v2
• LICENSE
• Maintenance Status

Installation

This module is distributed via npm which is bundled with node and should be installed as one of your project's dependencies:

# npm
npm install --save prism-react-renderer
# yarn
yarn add prism-react-renderer
# pnpm
pnpm add prism-react-renderer

Prism React Renderer has a peer dependency on react

Usage

Prism React Renderer has a named export for the <Highlight /> component along with themes. To see Prism React Render in action with base styling check out packages/demo or run pnpm run start:demo from the root of this repository.

import React from "react"
import ReactDOM from "react-dom/client"
import { Highlight, themes } from "prism-react-renderer"
import styles from 'styles.module.css'

const codeBlock = `
const GroceryItem: React.FC<GroceryItemProps> = ({ item }) => {
  return (
    <div>
      <h2>{item.name}</h2>
      <p>Price: {item.price}</p>
      <p>Quantity: {item.quantity}</p>
    </div>
  );
}
`

export const App = () => (
  <Highlight
    theme={themes.shadesOfPurple}
    code={codeBlock}
    language="tsx"
  >
    {({ className, style, tokens, getLineProps, getTokenProps }) => (
      <pre style={style}>
        {tokens.map((line, i) => (
          <div key={i} {...getLineProps({ line })}>
            <span>{i + 1}</span>
            {line.map((token, key) => (
              <span key={key} {...getTokenProps({ token })} />
            ))}
          </div>
        ))}
      </pre>
    )}
  </Highlight>
)

ReactDOM
  .createRoot(document.getElementById("root") as HTMLElement)
  .render(<App />)

Custom Language Support

By default prism-react-renderer only includes a base set of languages that Prism supports.

Note: Some languages (such as Javascript) are part of the bundle of other languages

Depending on your app's build system you may need to await the import or use require to ensure window.Prism exists before importing the custom languages. You can add support for more by including their definitions from the main prismjs package:

import { Highlight, Prism } from "prism-react-renderer";

(typeof global !== "undefined" ? global : window).Prism = Prism
await import("prismjs/components/prism-applescript")
/** or **/
require("prismjs/components/prism-applescript")

Basic Props

This is the list of props that you should probably know about. There are some advanced props below as well.

Most of these advanced props are included in the defaultProps.

children

function({}) | required

This is called with an object. Read more about the properties of this object in the section "Children Function".

language

string | required

This is the language that your code will be highlighted as. You can see a list of all languages that are supported out of the box here. Not all languages are included and the list of languages that are currently is a little arbitrary. You can use the escape-hatch to use your own Prism setup, just in case, or add more languages to the bundled Prism.

code

string | required

This is the code that will be highlighted.

Advanced Props

theme

PrismTheme | optional; default is vsDark

If a theme is passed, it is used to generate style props which can be retrieved via the prop-getters which are described in "Children Function".

Read more about how to theme prism-react-renderer in the section "Theming".

prism

prism | optional; default is the vendored version

This is the Prismjs library itself. A vendored version of Prism is provided (and also exported) as part of this library. This vendored version doesn't pollute the global namespace, is slimmed down, and doesn't conflict with any installation of prismjs you might have.

If you're only using Prism.highlight you can choose to use prism-react-renderer's exported, vendored version of Prism instead.

But if you choose to use your own Prism setup, simply pass Prism as a prop:

// Whichever way you're retrieving Prism here:
import Prism from 'prismjs/components/prism-core';

<Highlight prism={Prism} {/* ... */} />

Children Function

This is where you render whatever you want to based on the output of <Highlight />. You use it like so:

const ui = (
  <Highlight>
    {highlight => (
      // use utilities and prop getters here, like highlight.className, highlight.getTokenProps, etc.
      <pre>{/* more jsx here */}</pre>
    )}
  </Highlight>
);

The properties of this highlight object can be split into two categories as indicated below:

state

These properties are the flat output of <Highlight />. They're generally "state" and are what you'd usually expect from a render-props-based API.

A "Token" is an object that represents a piece of content for Prism. It has a types property, which is an array of types that indicate the purpose and styling of a piece of text, and a content property, which is the actual text.

You'd typically iterate over tokens, rendering each line, and iterate over its items, rendering out each token, which is a piece of this line.

prop getters

See Kent C. Dodds' blog post about prop getters

These functions are used to apply props to the elements that you render. This gives you maximum flexibility to render what, when, and wherever you like.

You'd typically call these functions with some dictated input and add on all other props that it should pass through. It'll correctly override and modify the props that it returns to you, so passing props to it instead of adding them directly is advisable.

getLineProps

You need to add a line property (type: Token[]) to the object you're passing to getLineProps.

This getter will return you props to spread onto your line elements (typically <div>s).

It will typically return a className (if you pass one it'll be appended), children, style (if you pass one it'll be merged). It also passes on all other props you pass to the input.

The className will always contain .token-line.

getTokenProps

You need to add a token property (type: Token) to the object you're passing to getTokenProps.

This getter will return you props to spread onto your token elements (typically <span>s).

It will typically return a className (if you pass one it'll be appended), children, style (if you pass one it'll be merged). It also passes on all other props you pass to the input.

The className will always contain .token. This also provides full compatibility with your old Prism CSS-file themes.

Utility Functions

useTokenize

(options: TokenizeOptions) => Token[][]

type TokenizeOptions = {
  prism: PrismLib
  code: string
  grammar?: PrismGrammar
  language: Language
}

This is a React hook that tokenizes code using Prism. It returns an array of tokens that can be rendered using the built-in <Highlight /> component or your own custom component. It uses normalizeTokens internally to convert the tokens into a shape that can be rendered.

• prism: PrismLib: the Prism library to use for tokenization. This can be the vendored version of Prism that is included with prism-react-renderer or a custom version of Prism that you have configured.

• code: string: a string containing the code to tokenize.

• grammar?: PrismGrammar: a Prism grammar object to use for tokenization. If this is omitted, the tokens will just be normalized. A grammar can be obtained from Prism.languages or by importing a language from prismjs/components/.

• language: Language: the language to use for tokenization. This should be a language that Prism supports.

normalizeTokens

(tokens: (PrismToken | string)[]) => Token[][]

Takes an array of Prism’s tokens and groups them by line, converting strings into tokens. Tokens can become recursive in some cases which means that their types are concatenated. Plain-string tokens however are always of type plain.

• PrismToken is an internal alias for Token exported by prismjs and is defined here.

• Token is an internal object that represents a slice of tokenized content for Prism with three properties:

  • types: string[]: an array of types that indicate the purpose and styling of a piece of text
  • content: string: the content of the token
  • empty: boolean: a flag indicating whether the token is empty or not.

Theming

The defaultProps you'd typically apply in a basic use-case, contain a default theme. This theme is vsDark.

While all classNames are provided with <Highlight />, so that you could use your good old Prism CSS-file themes, you can also choose to use prism-react-renderer's themes like so:

import { Highlight, themes } from 'prism-react-renderer';

<Highlight theme={themes.dracula} {/* ... */} />

These themes are JSON-based and are heavily inspired by VSCode's theme format.

Their syntax, expressed in Flow looks like the following:

{
  plain: StyleObj,
  styles: Array<{
    types: string[],
    languages?: string[],
    style: StyleObj
  }>
}

The plain property provides a base style-object. This style object is directly used in the style props that you'll receive from the prop getters, if a theme prop has been passed to <Highlight />.

The styles property contains an array of definitions. Each definition contains a style property, that is also just a style object. These styles are limited by the types and languages properties.

The types properties is an array of token types that Prism outputs. The languages property limits styles to highlighted languages.

When converting a Prism CSS theme it's mostly just necessary to use classes as types and convert the declarations to object-style-syntax and put them on style.

Upgrade

If you are migrating from v1.x to v2.x, follow these steps

Change module imports

- import Highlight, { defaultProps } from "prism-react-renderer";
+ import { Highlight } from "prism-react-renderer"

const Content = (
-  <Highlight {...defaultProps} code={exampleCode} language="jsx">
+  <Highlight code={exampleCode} language="jsx">

Change theme imports

- const theme = require('prism-react-renderer/themes/github')
+ const theme = require('prism-react-renderer').themes.github

Check language support

By default prism-react-renderer only includes a base set of languages that Prism supports. Depending on your app's build system you may need to await the import or use require to ensure window.Prism exists before importing the custom languages.

See: https://github.com/FormidableLabs/prism-react-renderer#custom-language-support

Install prismjs (if not available yet):

# npm
npm install --save prismjs
# yarn
yarn add prismjs
# pnpm
pnpm add prismjs

Add language component

If the language is not already bundled in the above, you can add additional languages with the following code:

import { Highlight, Prism } from "prism-react-renderer";

(typeof global !== "undefined" ? global : window).Prism = Prism
await import("prismjs/components/prism-applescript")
/** or **/
require("prismjs/components/prism-applescript")

LICENSE

MIT

Maintenance Status

Active: Nearform is actively working on this project, and we expect to continue work for the foreseeable future. Bug reports, feature requests and pull requests are welcome.