TypeScript transpiler for Node.js

README.md

Minimal TypeScript loader for Node.js

In newer versions of Node.js you can register your own loader and resolvers. This is an example of automatically transpiling .ts files.

Usage:

> node --import ./ts-loader.mjs ./my-app.ts

ts-loader-hooks.mjs

import { transform } from 'esbuild';
import { existsSync } from 'node:fs';
import { fileURLToPath } from 'node:url';

const isRelativeJs = /^\.{1,2}\/.+\.js$/;

/**
 * In TypeScript you can use .js extension in import statements, even though the actual file uses .ts
 * @see https://nodejs.org/api/module.html#resolvespecifier-context-nextresolve
 * @param {string} specifier
 * @param {Object} context
 * @param {Function} nextResolve
 */
export async function resolve(specifier, context, nextResolve) {
  if (isRelativeJs.test(specifier) && !existsSync(fileURLToPath(new URL(specifier, context.parentURL)))) {
    return nextResolve(specifier.replace(/\.js$/, '.ts'), context);
  }
  return nextResolve(specifier, context);
}

/**
 * Transpile .ts files using esbuild.
 * @see https://nodejs.org/api/module.html#loadurl-context-nextload
 * @param {string} url
 * @param {Object} context
 * @param {Function} nextLoad
 */
export async function load(url, context, nextLoad) {
  if (!url.endsWith('.ts')) return nextLoad(url, context);
  const { source, format } = await nextLoad(url, { ...context, format: 'module' });
  const { code } = await transform(source, { loader: 'ts' });
  return { source: code, format };
}

ts-loader.mjs

import { register } from 'node:module';

register(new URL('ts-loader-hooks.mjs', import.meta.url));