Amaro

Amaro is a wrapper around @swc/wasm-typescript, a WebAssembly port of the SWC TypeScript parser. 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.

How to Install

To install Amaro, run:

npm install amaro

How to Use

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';"

Loader

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.

Programmatic registration with module.register()

If you want TypeScript to "just work" in an existing codebase without passing --import every time, create a small bootstrap file and register Amaro once before loading your TS entrypoint.

// bootstrap.mjs
import { register } from "node:module";

register("amaro/strip", import.meta.url);
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.

Type stripping in dependencies

Contrary to the Node.js TypeScript support, when used as a loader, Amaro handles TypeScript files inside folders under a node_modules path.

Monorepo usage

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.

TypeScript Version

The supported TypeScript version is 5.8.

License (MIT)

See LICENSE.md.