Amaro is a Node.js wrapper around the SWC TypeScript parser and type stripper. Its Rust core in crates/amaro depends on the published SWC crates and is compiled to WebAssembly. It's used as an internal in Node.js for Type Stripping but can also be used as a standalone package.

Amaro means "bitter" in Italian. It's a reference to Mount Amaro on whose slopes this package was conceived.

This package provides a stable API for the TypeScript parser and allows users to upgrade to the latest version of TypeScript transpiler independently from the one used internally in Node.js.

The WebAssembly module is not checked in. Building it requires Docker, which runs the Rust build inside the Node.js wasm-builder container:

npm run build:wasm
npm run build
npm test

Releases build the module in CI before publishing.

To install Amaro, run:

npm install amaro

By default Amaro exports a transformSync function that performs type stripping. Stack traces are preserved, by replacing removed types with white spaces.

const amaro = require('amaro');
const { code } = amaro.transformSync("const foo: string = 'bar';", { mode: "strip-only" });
console.log(code); // "const foo         = 'bar';"

It is possible to use Amaro as an external loader to execute TypeScript files. This allows the installed Amaro to override the Amaro version used by Node.js. In order to use Amaro as an external loader, type stripping needs to be enabled.

node --import="amaro/strip" file.ts

In node v22.18.0 and later you can omit the --experimental-strip-types flag, as it is enabled by default.

Enabling TypeScript feature transformation:

node --enable-source-maps --import="amaro/transform" file.ts

Note that the amaro/transform loader should be used with --enable-source-maps to preserve accurate source-mapped stack traces.

Amaro's strip and transform entry points use module.registerHooks() to register synchronous hooks on Node.js versions that provide it, and fall back to module.register() on older versions. If you want TypeScript to "just work" in an existing codebase without passing --import every time, create a small bootstrap file that imports Amaro before loading your TS entrypoint.

// bootstrap.mjs
import "amaro/strip";
await import("./src/index.ts");

Then start your app through the bootstrap file:

node --watch ./bootstrap.mjs

For transform mode, swap amaro/strip with amaro/transform and run Node with --enable-source-maps.

Amaro makes working in monorepos smoother by removing the need to rebuild internal packages during development. When used with the --conditions flag, you can reference TypeScript source files directly in exports:

"exports": {
  ".": {
    "typescript": "./src/index.ts",
    "types": "./dist/index.d.ts",
    "require": "./dist/index.js",
    "import": "./dist/index.js"
 }
}

Then run your app with:

node --watch --import="amaro/strip" --conditions=typescript ./src/index.ts

This setup allows Node.js to load TypeScript files from linked packages without a build step. Changes to any package are picked up immediately, speeding up and simplifying local development in monorepos.

The supported TypeScript version is 5.8.

See LICENSE.md.