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teaganga
teaganga

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What is tsup?

#javascript #typescript #npm #webdev

tsup is a super-fast JavaScript/TypeScript bundler built on esbuild. It’s designed for libraries: minimal config, great defaults, and it can spit out ESM + CJS builds (and type declarations) in one go.

Why people use tsup

  • 🚀 Speed (esbuild under the hood)
  • 🧩 Zero/low config (works from the CLI or a tiny config file)
  • 📦 Dual output (esm + cjs) for broad compatibility
  • 📝 Type defs: can emit .d.ts with dts: true
  • 🔧 Nice extras: watch mode, minify, treeshake, code splitting, sourcemaps

Quick start 

npm i -D tsup typescript
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package.json

{ "scripts": { "build": "tsup", "dev": "tsup --watch", "prepare": "npm run build" } }
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tsup.config.ts

import { defineConfig } from 'tsup'; export default defineConfig({ entry: ['src/index.ts'], format: ['esm', 'cjs'], dts: true, // emit .d.ts sourcemap: true, clean: true, target: 'es2020', treeshake: true });
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tsconfig.json (minimal)

{ "compilerOptions": { "target": "ES2020", "moduleResolution": "bundler", "strict": true, "declaration": true, "emitDeclarationOnly": false, "skipLibCheck": true }, "include": ["src"] }
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Run:

npm run build
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You’ll get dist/index.mjs, dist/index.cjs, and dist/index.d.ts.

How it compares

  • tsc: compiles TS → JS, but doesn’t bundle (each file out). tsup bundles your code (and can mark deps as external).
  • rollup/webpack: very flexible; more config. tsup is “rollup-lite” for libs—fast and simple.
  • vite: great for apps/dev servers; you can build libs, but tsup is often simpler for publishing packages.

When to use / not use

  • Use tsup for publishing libraries quickly with dual builds + types.
  • If you need exotic bundling (custom plugins, unusual module targets), rollup/webpack may still be better.
  • If you want no bundling at all, just tsc might suffice.

Conclusion

That’s it—tsup = fast, simple library bundling with type definitions baked in.

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