TS and node.js support

References

• https://nodejs.org/api/typescript.html#enabling
• https://your-ehsan.medium.com/10-mind-blowing-node-js-features-that-make-it-unstoppable-86a5e98e2fc2

Examples

Versions

➜  ts-nodesupport git:(main) node --version
v23.5.0
➜  ts-nodesupport git:(main) npm --version
10.9.2

Disable ExperimentalWarning --disable-warning=ExperimentalWarning

➜  ts-nodesupport git:(main) cat hellots.ts 
function foo(bar: number): string {
  return 'hello';
}
console.log(foo(4));
➜  ts-nodesupport git:(main) npm run ts hellots.ts

> nodesupport@1.0.0 ts
> node --experimental-transform-types --disable-warning=ExperimentalWarning hellots.ts

hello

Disable warnings --no-warnings

➜  ts-nodesupport git:(main) cat simple.ts 
type User = {
  name: string;
  age: number;
};

function isAdult(user: User): boolean {
  return user.age >= 18;
}

// Unlike type assertions (`as`), `satisfies` does not change the type of the object but 
// ensures it meets the requirements of the specified type.
const justine = {
  name: 'Justine',
  age: 23,
} satisfies User; 

const isJustineAnAdult = isAdult(justine);

console.log(isJustineAnAdult);

➜  ts-nodesupport git:(main) ✗ npm start simple.ts

> nodesupport@1.0.0 start
> node --experimental-transform-types --no-warnings simple.ts

true

Type Stripping

1. By default Node.js will execute TypeScript files that contains only erasable TypeScript syntax.

2. Node.js will replace TypeScript syntax with whitespace, and no type checking is performed.

3. To enable the transformation of non erasable TypeScript syntax, which requires JavaScript code generation, such as

   1. enum declarations,
   2. parameter properties

   use the flag --experimental-transform-types. To disable this feature, use the flag --no-experimental-strip-types.

Watch Mode

The --watch flag enables automatic re-running of your code whenever files change. This means you no longer need to use nodemon or manually restart your tests or applications.

Simply run your tests with the --watch flag, and Node.js will monitor your files for any changes, automatically re-running the tests upon saving.

➜  ts-nodesupport git:(main) ✗ node --help | grep watch
  --watch                     run in watch mode
  --watch-path=...            path to watch
  --watch-preserve-output     preserve outputs on watch mode restart

env-file Flag

Node.js now supports loading environment variables directly from a specified .env file using the --env-file flag. This feature allows you to manage your environment variables more effectively without needing additional libraries.

➜  ts-nodesupport git:(main) ✗ node --help | grep env-file
  --env-file=...              set environment variables from supplied
  --env-file-if-exists=...    set environment variables from supplied

Top level Await

With the latest updates, Node.js now supports top-level await, allowing you to use the await keyword outside of an async function. This simplifies writing asynchronous code and improves readability.

✗ ./top-level-await.mts
#!/usr/bin/env node --experimental-transform-types --disable-warning=ExperimentalWarning --env-file=.env

import { readFile } from "fs/promises";

const contents = await readFile("./top-level-await.mts", "utf-8");
console.log(contents)