🎨 react-shiki

A performant client-side syntax highlighting component and hook for React, built with Shiki.

See the demo page with highlighted code blocks showcasing several Shiki themes!

• 🎨 react-shiki
  • Features
  • Installation
  • Usage
  • Bundle Options
    • react-shiki (Full Bundle)
    • react-shiki/web (Web Bundle)
    • react-shiki/core (Minimal Bundle)
    • RegExp Engines
  • Configuration
    • Common Configuration Options
    • Component-specific Props
    • Multi-theme Support
      • Making Themes Reactive
        • Option 1: Using light-dark() Function (Recommended)
        • Option 2: CSS Theme Switching
    • Custom Themes
    • Custom Languages
      • Preloading Custom Languages
    • Language Aliases
    • Custom Transformers
    • Line Numbers
  • Integration
    • Integration with react-markdown
    • Handling Inline Code
  • Performance
    • Throttling Real-time Highlighting
    • Output Format Optimization
    • Streaming and LLM Chat UI

Features

• 🖼️ Provides both a ShikiHighlighter component and a useShikiHighlighter hook for more flexibility
• 🔐 Flexible output: Choose between React elements (no dangerouslySetInnerHTML) or HTML strings for better performance
• 📦 Multiple bundle options: Full bundle (~1.2MB gz), web bundle (~695KB gz), or minimal core bundle for fine-grained bundle control
• 🖌️ Full support for custom TextMate themes and languages
• 🔧 Supports passing custom Shiki transformers to the highlighter, in addition to all other options supported by codeToHast
• 🚰 Performant highlighting of streamed code, with optional throttling
• 📚 Includes minimal default styles for code blocks
• 🚀 Shiki dynamically imports only the languages and themes used on a page for optimal performance
• 🖥️ ShikiHighlighter component displays a language label for each code block when showLanguage is set to true (default)
• 🎨 Customizable styling of generated code blocks and language labels
• 📏 Optional line numbers with customizable starting number and styling

Installation

npm i react-shiki

Usage

You can use either the ShikiHighlighter component or the useShikiHighlighter hook to highlight code.

Using the Component:

import ShikiHighlighter from "react-shiki";

function CodeBlock() {
  return (
    <ShikiHighlighter language="jsx" theme="ayu-dark">
      {code.trim()}
    </ShikiHighlighter>
  );
}

Using the Hook:

import { useShikiHighlighter } from "react-shiki";

function CodeBlock({ code, language }) {
  const highlightedCode = useShikiHighlighter(code, language, "github-dark");

  return <div className="code-block">{highlightedCode}</div>;
}

Bundle Options

react-shiki, like shiki, offers three entry points to balance convenience and bundle optimization:

react-shiki (Full Bundle)

import ShikiHighlighter from 'react-shiki';

• Size: ~6.4MB minified, ~1.2MB gzipped (includes ~12KB react-shiki)
• Languages: All Shiki languages and themes
• Exported engines: createJavaScriptRegexEngine, createJavaScriptRawEngine
• Use case: Unknown language requirements, maximum language support
• Setup: Zero configuration required

react-shiki/web (Web Bundle)

import ShikiHighlighter from 'react-shiki/web';

• Size: ~3.8MB minified, ~707KB gzipped (includes ~12KB react-shiki)
• Languages: Web-focused languages (HTML, CSS, JS, TS, JSON, Markdown, Vue, JSX, Svelte)
• Exported engines: createJavaScriptRegexEngine, createJavaScriptRawEngine
• Use case: Web applications with balanced size/functionality
• Setup: Drop-in replacement for main entry point

react-shiki/core (Minimal Bundle)

import ShikiHighlighter, { 
  createHighlighterCore,        // re-exported from shiki/core
  createOnigurumaEngine,        // re-exported from shiki/engine/oniguruma
  createJavaScriptRegexEngine,  // re-exported from shiki/engine/javascript
} from 'react-shiki/core';

// Create custom highlighter with dynamic imports to optimize client-side bundle size
const highlighter = await createHighlighterCore({
  themes: [import('@shikijs/themes/nord')],
  langs: [import('@shikijs/langs/typescript')],
  engine: createOnigurumaEngine(import('shiki/wasm')) 
    // or createJavaScriptRegexEngine()
});

<ShikiHighlighter highlighter={highlighter} language="typescript" theme="nord">
  {code}
</ShikiHighlighter>

• Size: ~12KB + your imported themes/languages
• Languages: User-defined via custom highlighter
• Use case: Production apps requiring maximum bundle control
• Setup: Requires custom highlighter configuration
• Engine options: Choose JavaScript engine (smaller bundle, faster startup) or Oniguruma (WASM, maximum language support)

RegExp Engines

Shiki offers three built-in engines for syntax highlighting:

• Oniguruma - Default engine using compiled WebAssembly, offers maximum language support
• JavaScript RegExp - Smaller bundle, faster startup, compiles patterns on-the-fly, recommended for client-side highlighting
• JavaScript Raw - For pre-compiled languages, skips transpilation step for best performance

Using Engines with Full and Web Bundles

The full and web bundles use Oniguruma by default, but you can override this with the engine option:

import {
  useShikiHighlighter,
  createJavaScriptRegexEngine,
  createJavaScriptRawEngine
} from 'react-shiki';

// Hook with JavaScript RegExp engine
const highlightedCode = useShikiHighlighter(code, 'typescript', 'github-dark', {
  engine: createJavaScriptRegexEngine()
});

// Component with JavaScript Raw engine (for pre-compiled languages)
// See https://shiki.style/guide/regex-engines#pre-compiled-languages
<ShikiHighlighter
  language="typescript"
  theme="github-dark"
  engine={createJavaScriptRawEngine()}
>
  {code}
</ShikiHighlighter>

Using Engines with Core Bundle

When using the core bundle, you must specify an engine:

import {
  createHighlighterCore,
  createOnigurumaEngine,
  createJavaScriptRegexEngine
} from 'react-shiki/core';

const highlighter = await createHighlighterCore({
  themes: [import('@shikijs/themes/nord')],
  langs: [import('@shikijs/langs/typescript')],
  engine: createJavaScriptRegexEngine() // or createOnigurumaEngine(import('shiki/wasm'))
});

Engine Options

The JavaScript RegExp engine is strict by default. For best-effort results with unsupported grammars, enable the forgiving option:

createJavaScriptRegexEngine({ forgiving: true });

See Shiki - RegExp Engines for more info.

Configuration

Common Configuration Options

| Option | Type | Default | Description | | ------------------- | ------------------ | --------------- | ----------------------------------------------------------------------------- | | code | string | - | Code to highlight | | language | string \| object | - | Language to highlight, built-in or custom textmate grammer object | | theme | string \| object | 'github-dark' | Single or multi-theme configuration, built-in or custom textmate theme object | | delay | number | 0 | Delay between highlights (in milliseconds) | | customLanguages | array | [] | Array of custom languages to preload | | langAlias | object | {} | Map of language aliases | | engine | RegexEngine | Oniguruma | RegExp engine for syntax highlighting (Oniguruma, JavaScript RegExp, or JavaScript Raw) | | showLineNumbers | boolean | false | Display line numbers alongside code | | startingLineNumber | number | 1 | Starting line number when line numbers are enabled | | transformers | array | [] | Custom Shiki transformers for modifying the highlighting output | | cssVariablePrefix | string | '--shiki' | Prefix for CSS variables storing theme colors | | defaultColor | string \| false | 'light' | Default theme mode when using multiple themes, can also disable default theme | | outputFormat | string | 'react' | Output format: 'react' for React nodes, 'html' for HTML string | | tabindex | number | 0 | Tab index for the code block | | decorations | array | [] | Custom decorations to wrap the highlighted tokens with | | structure | string | classic | The structure of the generated HAST and HTML - classic or inline | | codeToHastOptions | - | - | All other options supported by Shiki's codeToHast |

Component-specific Props

The ShikiHighlighter component offers minimal built-in styling and customization options out-of-the-box:

| Prop | Type | Default | Description | | ------------------ | --------- | ------- | ---------------------------------------------------------- | | showLanguage | boolean | true | Displays language label in top-right corner | | addDefaultStyles | boolean | true | Adds minimal default styling to the highlighted code block | | as | string | 'pre' | Component's Root HTML element | | className | string | - | Custom class name for the code block | | langClassName | string | - | Class name for styling the language label | | style | object | - | Inline style object for the code block | | langStyle | object | - | Inline style object for the language label |

Multi-theme Support

To use multiple theme modes, pass an object with your multi-theme configuration to the theme prop in the ShikiHighlighter component:

<ShikiHighlighter
  language="tsx"
  theme={{
    light: "github-light",
    dark: "github-dark",
    dim: "github-dark-dimmed",
  }}
  defaultColor="dark"
>
  {code.trim()}
</ShikiHighlighter>

Or, when using the hook, pass it to the theme parameter:

const highlightedCode = useShikiHighlighter(
  code,
  "tsx",
  {
    light: "github-light",
    dark: "github-dark",
    dim: "github-dark-dimmed",
  },
  {
    defaultColor: "dark",
  }
);

Making Themes Reactive

There are two approaches to make multi-themes reactive to your site's theme:

Option 1: Using light-dark() Function (Recommended)

Set defaultColor="light-dark()" to use CSS's built-in light-dark() function. This automatically switches themes based on the user's color-scheme preference:

// Component
<ShikiHighlighter
  language="tsx"
  theme={{
    light: "github-light",
    dark: "github-dark",
  }}
  defaultColor="light-dark()"
>
  {code.trim()}
</ShikiHighlighter>

// Hook
const highlightedCode = useShikiHighlighter(code, "tsx", {
  light: "github-light",
  dark: "github-dark",
}, {
  defaultColor: "light-dark()"
});

Ensure your site sets the color-scheme CSS property:

:root {
  color-scheme: light dark;
}

/* Or dynamically for class based dark mode */
:root {
  color-scheme: light;
}

:root.dark {
  color-scheme: dark;
}

Option 2: CSS Theme Switching

For broader browser support or more control, add CSS snippets to your site to enable theme switching with media queries or class-based switching. See Shiki's documentation for the required CSS snippets.

Note: The light-dark() function requires modern browser support. For older browsers, use the manual CSS variables approach.

Custom Themes

Custom themes can be passed as a TextMate theme in JavaScript object. For example, it should look like this.

import tokyoNight from "../styles/tokyo-night.json";

// Component
<ShikiHighlighter language="tsx" theme={tokyoNight}>
  {code.trim()}
</ShikiHighlighter>

// Hook
const highlightedCode = useShikiHighlighter(code, "tsx", tokyoNight);

Custom Languages

Custom languages should be passed as a TextMate grammar in JavaScript object. For example, it should look like this

import mcfunction from "../langs/mcfunction.tmLanguage.json";

// Component
<ShikiHighlighter language={mcfunction} theme="github-dark">
  {code.trim()}
</ShikiHighlighter>

// Hook
const highlightedCode = useShikiHighlighter(code, mcfunction, "github-dark");

Preloading Custom Languages

For dynamic highlighting scenarios where language selection happens at runtime:

import mcfunction from "../langs/mcfunction.tmLanguage.json";
import bosque from "../langs/bosque.tmLanguage.json";

// Component
<ShikiHighlighter
  language="typescript"
  theme="github-dark"
  customLanguages={[mcfunction, bosque]}
>
  {code.trim()}
</ShikiHighlighter>

// Hook
const highlightedCode = useShikiHighlighter(code, "typescript", "github-dark", {
  customLanguages: [mcfunction, bosque],
});

Language Aliases

You can define custom aliases for languages using the langAlias option. This is useful when you want to use alternative names for languages:

// Component
<ShikiHighlighter 
  language="indents" 
  theme="github-dark" 
  langAlias={{ indents: "python" }}
>
  {code.trim()}
</ShikiHighlighter>

// Hook
const highlightedCode = useShikiHighlighter(code, "indents", "github-dark", {
  langAlias: { indents: "python" },
});

Custom Transformers

import { customTransformer } from "../utils/shikiTransformers";

// Component
<ShikiHighlighter language="tsx" transformers={[customTransformer]}>
  {code.trim()}
</ShikiHighlighter>

// Hook
const highlightedCode = useShikiHighlighter(code, "tsx", "github-dark", {
  transformers: [customTransformer],
});

Line Numbers

Display line numbers alongside your code, these are CSS-based and can be customized with CSS variables:

// Component
<ShikiHighlighter 
  language="javascript"
  theme="github-dark"
  showLineNumbers,
  startingLineNumber={0} // default is 1
>
  {code}
</ShikiHighlighter>

<ShikiHighlighter 
  language="python" 
  theme="github-dark" 
  showLineNumbers 
  startingLineNumber={0}
>
  {code}
</ShikiHighlighter>

// Hook (import 'react-shiki/css' for line numbers to work)
const highlightedCode = useShikiHighlighter(code, "javascript", "github-dark", {
  showLineNumbers: true,
  startingLineNumber: 0, 
});

[!NOTE] When using the hook with line numbers, import the CSS file for the line numbers to work:

import 'react-shiki/css';

Or provide your own CSS counter implementation and styles for .line-numbers (line span) and .has-line-numbers (container code element)

Available CSS variables for customization:

--line-numbers-foreground: rgba(107, 114, 128, 0.5);
--line-numbers-width: 2ch;
--line-numbers-padding-left: 0ch;
--line-numbers-padding-right: 2ch;
--line-numbers-font-size: inherit;
--line-numbers-font-weight: inherit;
--line-numbers-opacity: 1;

You can customize them in your own CSS or by using the style prop on the component:

<ShikiHighlighter 
  language="javascript"
  theme="github-dark"
  showLineNumbers
  style={{
    '--line-numbers-foreground': '#60a5fa',
    '--line-numbers-width': '3ch'
  }}
>
  {code}
</ShikiHighlighter>

Integration

Integration with react-markdown

Create a component to handle syntax highlighting:

import ReactMarkdown from "react-markdown";
import ShikiHighlighter, { isInlineCode } from "react-shiki";

const CodeHighlight = ({ className, children, node, ...props }) => {
  const code = String(children).trim();
  const match = className?.match(/language-(\w+)/);
  const language = match ? match[1] : undefined;
  const isInline = node ? isInlineCode(node) : undefined;

  return !isInline ? (
    <ShikiHighlighter language={language} theme="github-dark" {...props}>
      {code}
    </ShikiHighlighter>
  ) : (
    <code className={className} {...props}>
      {code}
    </code>
  );
};

Pass the component to react-markdown as a code component:

<ReactMarkdown
  components={{
    code: CodeHighlight,
  }}
>
  {markdown}
</ReactMarkdown>

Handling Inline Code

Prior to 9.0.0, react-markdown exposed the inline prop to code components which helped to determine if code is inline. This functionality was removed in 9.0.0. For your convenience, react-shiki provides two ways to replicate this functionality and API.

Method 1: Using the isInlineCode helper:

react-shiki exports isInlineCode which parses the node prop from react-markdown and identifies inline code by checking for the absence of newline characters:

import ShikiHighlighter, { isInlineCode } from "react-shiki";

const CodeHighlight = ({ className, children, node, ...props }) => {
  const match = className?.match(/language-(\w+)/);
  const language = match ? match[1] : undefined;

  const isInline = node ? isInlineCode(node) : undefined;

  return !isInline ? (
    <ShikiHighlighter language={language} theme="github-dark" {...props}>
      {String(children).trim()}
    </ShikiHighlighter>
  ) : (
    <code className={className} {...props}>
      {children}
    </code>
  );
};

Method 2: Using the rehypeInlineCodeProperty plugin:

react-shiki also exports rehypeInlineCodeProperty, a rehype plugin that provides the same API as react-markdown prior to 9.0.0. It reintroduces the inline prop which works by checking if <code> is nested within a <pre> tag, if not, it's considered inline code and the inline prop is set to true.

It's passed as a rehypePlugin to react-markdown:

import ReactMarkdown from "react-markdown";
import { rehypeInlineCodeProperty } from "react-shiki";

<ReactMarkdown
  rehypePlugins={[rehypeInlineCodeProperty]}
  components={{
    code: CodeHighlight,
  }}
>
  {markdown}
</ReactMarkdown>;

Now inline can be accessed as a prop in the code component:

const CodeHighlight = ({
  inline,
  className,
  children,
  node,
  ...props
}: CodeHighlightProps): JSX.Element => {
  const match = className?.match(/language-(\w+)/);
  const language = match ? match[1] : undefined;
  const code = String(children).trim();

  return !inline ? (
    <ShikiHighlighter language={language} theme="github-dark" {...props}>
      {code}
    </ShikiHighlighter>
  ) : (
    <code className={className} {...props}>
      {code}
    </code>
  );
};

Performance

Throttling Real-time Highlighting

For improved performance when highlighting frequently changing code:

// With the component
<ShikiHighlighter language="tsx" theme="github-dark" delay={150}>
  {code.trim()}
</ShikiHighlighter>

// With the hook
const highlightedCode = useShikiHighlighter(code, "tsx", "github-dark", {
  delay: 150,
});

Output Format Optimization

react-shiki provides two output formats to balance safety and performance:

React Nodes (Default) - Safer, no dangerouslySetInnerHTML required

// Hook
const highlightedCode = useShikiHighlighter(code, "tsx", "github-dark");

// Component
<ShikiHighlighter language="tsx" theme="github-dark">
  {code}
</ShikiHighlighter>

HTML String - 15-45% faster performance

// Hook (returns HTML string, use dangerouslySetInnerHTML to render)
const highlightedCode = useShikiHighlighter(code, "tsx", "github-dark", {
  outputFormat: 'html'
});

// Component (automatically uses dangerouslySetInnerHTML when outputFormat is 'html')
<ShikiHighlighter language="tsx" theme="github-dark" outputFormat="html">
  {code}
</ShikiHighlighter>

Choose HTML output when performance is critical and you trust the code source. Use the default React output when handling untrusted content or when security is the primary concern.

Made with ❤️ by Bassim (AVGVSTVS96)