TypeScript with NodeJS

TypeScript has had first class support for NodeJS since inception. Here's how to setup a quick NodeJS project:

Note: many of these steps are actually just common practice nodejs setup steps

  1. Setup a nodejs 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 (node ./node_modules/typescript/lib/tsc --init)
  5. Make sure you have compilerOptions.module:commonjs in your tsconfig.json

That's it! Fire up your IDE (e.g. alm -o) and play around. Now you can use all the built in node modules (e.g. import fs = require('fs');) with all the safety and developer ergonomics of TypeScript!

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:live": "nodemon --exec ./node_modules/.bin/ts-node -- ./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.

Creating TypeScript node modules

Using modules written in TypeScript is super fun as you get great compile time safety and autocomplete (essentially executable documentation).

Creating a high quality TypeScript module is simple. Assume the following desired folder structure for your package:

package
├─ package.json
├─ tsconfig.json
├─ src
│  ├─ All your source files
│  ├─ index.ts
│  ├─ foo.ts
│  └─ ...
└─ lib
  ├─ All your compiled files
  ├─ index.d.ts
  ├─ index.js
  ├─ foo.d.ts
  ├─ foo.js
  └─ ...
  • In your tsconfig.json

    • have compilerOptions: "outDir": "lib" and "declaration": true < This generates declaration and js files in the lib folder
    • Include all the files from src < This includes all the files from the src dir.
  • In your package.json have

    • "main": "lib/index" < This tells NodeJS to load lib/index.js
    • "types": "lib/index" < This tells TypeScript to load lib/index.d.ts

Example package:

  • npm install typestyle for TypeStyle
  • Usage: import { style } from 'typestyle'; will be completely type safe.

MORE:

  • If you package depends on other TypeScript authored packages, put them in dependencies/devDependencies/peerDependencies just like you would with raw JS packages.
  • If you package depends on other JavaScript authored packages and you want to use it type safely in your project, put their types e.g. @types/foo in devDependencies. JavaScript types should be managed out of bound from the main NPM streams. The JavaScript ecosystem breaks types without semantic versioning too commonly, so if your users need types for these they should install the @types/foo version that works for them.

Bonus points

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

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