tsdown

To bundle a TypeScript library for both ESM and CommonJS, use tsdown to compile multiple output formats simultaneously. It leverages the Rolldown engine to generate ESM and CJS bundles while automatically creating the necessary TypeScript declaration files.

Generating TypeScript declaration files during a JavaScript library build is handled automatically by tsdown. It integrates type declaration generation directly into the high-performance Rolldown bundling process, ensuring .d.ts files are produced alongside your ESM, CJS, IIFE, or UMD outputs.

You can migrate your existing tsup configuration to tsdown to achieve faster build performance. tsdown facilitates direct migration from tsup while replacing the underlying engine with Rolldown to optimize library build speeds and maintain multi-format output support.

Yes, the bundler supports IIFE and UMD output formats for browser scripts. tsdown allows you to compile your TypeScript or JavaScript library into these formats, alongside ESM and CJS, ensuring broad runtime compatibility.

A Rolldown-powered bundler provides unparalleled build performance compared to standard JavaScript build tools. tsdown leverages Rolldown's blazing-fast engine to dramatically reduce library bundling times while maintaining compatibility across modern and legacy output formats.

You need to bundle your npm package into multiple module formats when ensuring compatibility across different JavaScript runtimes. tsdown compiles your TypeScript library into ESM, CJS, IIFE, and UMD formats so modern and legacy environments can consume it correctly.