React Syntax Highlighter

React Syntax Highlighter is a component library that renders syntax-highlighted code blocks inside React applications. Instead of manually manipulating the DOM in componentDidMount/componentDidUpdate and injecting HTML with dangerouslySetInnerHTML, it walks an abstract syntax tree produced by highlight.js (via lowlight) or Prism (via refractor) and builds it into the virtual DOM, so updates only touch the nodes that actually changed and the component works as an idiomatic, pure function component.

All bundled styles are plain JavaScript objects rather than CSS files, so consumers get out-of-the-box code theming without adding a stylesheet <link> tag — every highlight.js and Prism theme has been ported to JS. Teams that prefer CSS classes instead can opt out with useInlineStyles={false}. A “light build” variant lets consumers register only the specific languages and styles they need to keep bundle size down, and async variants defer loading the highlighting engine and language definitions via dynamic import() for faster first paint.

What You Get

• A default SyntaxHighlighter component backed by highlight.js/lowlight, plus a Prism variant backed by refractor for better JSX and TSX highlighting fidelity
• Every highlight.js and Prism theme pre-ported to JavaScript style objects, importable directly from react-syntax-highlighter/dist/esm/styles/{hljs|prism}
• Light/PrismLight builds that only bundle languages you explicitly registerLanguage(), keeping bundle size small for apps that only need a handful of languages
• LightAsync/PrismAsyncLight/PrismAsync variants that dynamically import() the highlighting engine and language grammars for faster initial page loads
• Line-number rendering (showLineNumbers, showInlineLineNumbers), custom line wrapping (wrapLines, wrapLongLines), and per-line prop injection (lineProps) for building diff- or annotation-style code views
• A pluggable renderer prop and custom PreTag/CodeTag overrides for non-DOM targets (e.g. virtualized lists, React Native renderers)

Common Use Cases

• Rendering highlighted code snippets inside documentation sites, blog posts, or MDX content
• Building an in-app code viewer/diff viewer for developer tools, IDE-in-the-browser products, or PR review UIs
• Displaying generated or example code inside a design-system playground, API reference, or interactive tutorial
• Presentation/slide tools (e.g. mdx-deck) and Electron-based documentation editors that need themeable code blocks without a CSS build step

Under The Hood

Architecture src/index.js exports a family of components — the default highlight.js-backed SyntaxHighlighter, Light/PrismLight register-only-what-you-use builds, and LightAsync/PrismAsync/PrismAsyncLight dynamic-import variants — all funneling into the ~440-line src/highlight.js, which walks the AST returned by lowlight (highlight.js) or refractor (Prism) and recursively converts it into React elements via create-element.js (~210 lines), handling line numbers, line wrapping, and custom renderers along the way. async-syntax-highlighter.js (~155 lines) wraps the synchronous highlighter so language/theme modules can be code-split, rendering plain unhighlighted text with line numbers as a fallback while the import resolves.

Tech Stack Plain JavaScript compiled with Babel (no TypeScript in the source; types ship separately via DefinitelyTyped’s @types/react-syntax-highlighter), dual-published as CJS and ESM (build:cjs/build:esm) plus a webpack UMD bundle. Highlighting is delegated to highlight.js/lowlight and prismjs/refractor, with highlightjs-vue covering Vue templates; React itself is only a peer dependency (>= 0.14.0), so the library stays agnostic to the consumer’s React version.

Code Quality 20 Jest test files under __tests__/ use react-test-renderer snapshots to cover the async, light, and Prism variants, line-number rendering, custom pre/code tags, line wrapping, and unusual inputs (unknown language, plain text, Vue). Coverage is broad but mostly snapshot-based rather than fine-grained behavioral assertions. ESLint, Prettier, and husky/lint-staged enforce style at commit time; per the health-score data, recent commit velocity is low relative to the project’s age despite fairly regular point releases.

API Design The public API is declarative and low-boilerplate — <SyntaxHighlighter language="js" style={theme}>{code}</SyntaxHighlighter> is enough to get syntax highlighting working, and switching highlighting engine or loading strategy (sync/light/async) is a matter of swapping the import rather than learning a new API. The README documents every prop in one place with live demo links, though supported languages/styles are discoverable only via separate markdown reference files rather than editor autocomplete in the base package.