TypeScript with Node.js

TypeScript has had first class support for Node.js since inception. Here’s how to setup a quick Node.js project:

Note: many of these steps are actually just common practice Node.js setup steps

1. Setup a Node.js project package.json. Quick one : npm init -y
2. Add TypeScript (npm install typescript --save-dev)
3. Add node.d.ts (npm install @types/node --save-dev)
4. Init a tsconfig.json for TypeScript options with a few key options in your tsconfig.json (npx tsc --init --rootDir src --outDir lib --esModuleInterop --resolveJsonModule --lib es6,dom --module commonjs)

That’s it! Fire up your IDE (e.g. code .) and play around. Now you can use all the built in node modules (e.g. import * as fs from 'fs';) with all the safety and developer ergonomics of TypeScript!

All your TypeScript code goes in src and the generated JavaScript goes in lib.

Bonus: Live compile + run

• Add ts-node which we will use for live compile + run in node (npm install ts-node --save-dev)
• Add nodemon which will invoke ts-node whenever a file is changed (npm install nodemon --save-dev)

Now just add a script target to your package.json based on your application entry e.g. assuming its index.ts:

  "scripts": {
    "start": "npm run build:live",
    "build": "tsc -p .",
    "build:live": "nodemon --watch 'src/**/*.ts' --exec \"ts-node\" src/index.ts"
  },

So you can now run npm start and as you edit index.ts:

• nodemon reruns its command (ts-node)
• ts-node transpiles automatically picking up tsconfig.json and the installed TypeScript version,
• ts-node runs the output JavaScript through Node.js.

And when you are ready to deploy your JavaScript application run npm run build.

Node style callbacks

Node style callback functions (e.g. (err,somethingElse)=>{ /* something */ }) are generally called with err set to null if there isn’t an error. You generally just use a truthy check for this anyways:

fs.readFile('someFile', 'utf8', (err,data) => {
  if (err) {
    // do something
  } else {
    // no error
  }
});

When creating your own APIs it’s okay to use null in this case for consistency. In all sincerity for your own APIs you should look at promises, in that case you actually don’t need to bother with absent error values (you handle them with .then vs. .catch).

Bonus points

Such NPM modules work just fine with browserify (using tsify) or webpack (using ts-loader).

Nodejs-projects