#TypeScript

Build TypeScript browser extensions with zero custom bundler wiring.

Extension.js supports TypeScript across extension contexts (background, content scripts, and page scripts) using the default Rspack + SWC pipeline.

#When TypeScript is a good fit

• You want safer refactors and clearer contracts across extension contexts.
• You share logic between background scripts, content scripts, and UI surfaces.
• You need predictable API usage when working with AI-generated code.

#Template examples

#new-typescript

Best for building a new-tab extension with TypeScript defaults already configured.

npx extension@latest create my-extension --template=new-typescript

pnpx extension@latest create my-extension --template=new-typescript

yarn dlx extension@latest create my-extension --template=new-typescript

Repository: extension-js/examples/new-typescript

#content-typescript

Best for injecting TypeScript-powered content scripts into existing pages.

npx extension@latest create my-extension --template=content-typescript

pnpx extension@latest create my-extension --template=content-typescript

yarn dlx extension@latest create my-extension --template=content-typescript

Repository: extension-js/examples/content-typescript

#Using TypeScript with an existing extension

If you want to add TypeScript support to an existing extension, follow these steps.

#Installation

1. Install TypeScript as a development dependency:

npm install -D typescript

yarn add -D typescript

pnpm add -D typescript

bun add -D typescript

deno add -D npm:typescript

2. Initialize the TypeScript config file tsconfig.json:

npm tsc --init

yarn tsc --init

pnpm tsc --init

bun tsc --init

deno tsc --init

#Configuration

#TypeScript detection and requirements

Extension.js looks for tsconfig.json next to your package.json.

• If TypeScript source files are present and tsconfig.json is missing, Extension.js throws an error and asks you to create one.
• If TypeScript is detected through dependencies/config flow without source files, Extension.js can scaffold a baseline tsconfig.json.

Example baseline config:

{
  compilerOptions: {
    allowJs: true,
    allowSyntheticDefaultImports: true,
    esModuleInterop: true,
    forceConsistentCasingInFileNames: true,
    isolatedModules: false,
    jsx: 'react-jsx',
    lib: ['dom', 'dom.iterable', 'esnext'],
    moduleResolution: 'node',
    module: 'esnext',
    noEmit: true,
    resolveJsonModule: true,
    strict: true,
    target: 'esnext',
    skipLibCheck: true
  },
  exclude: ['node_modules', 'dist']
}

#Automatic types

Extension.js generates extension-env.d.ts in your project root (dev flow) with references to Extension.js ambient types and polyfill types.

// Required Extension.js types for TypeScript projects.
// This file is auto-generated and should not be excluded.
// If you need additional types, consider creating a new *.d.ts file and
// referencing it in the "include" array of your tsconfig.json file.
// See https://www.typescriptlang.org/tsconfig#include for more information.
/// <reference types="extension/types" />

// Polyfill types for browser.* APIs.
/// <reference types="extension/types/polyfill" />

#Transpilation vs type-checking

The default bundler pipeline transpiles TypeScript but does not run full tsc type-checking as part of bundling.

Recommended scripts:

{
  "scripts": {
    "dev": "extension dev",
    "typecheck": "tsc --noEmit"
  }
}

#Next steps

• Learn how Extension.js handles ECMAScript Modules.
• Explore styling options like Sass modules.

#Video walkthrough