Library setup

In this article, you'll learn how to create a typescript shared library that can be used in multiple projects simultaneously, which can be pretty helpful, especially when it comes to mono repositories.

First create a lib project:

mkdir lib-app && cd lib-app

Init npm:

npm init --yes

Update package.json to have the following properties and values:

{
  "name": "lib-app",
  "version": "1.0.0",
  "description": "A simple math library.",
  "main": "lib/index.js",
  "types": "lib",
  "scripts": {
    "build": "tsc p ."
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}

Install typescript as a dev dependency:

npm install typescript --save-dev

Init a typescript project:

npx tsc --init

Update tsconfig.json to the following:

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "commonjs",
    "declaration": true,
    "declarationMap": true,
    "outDir": "lib",
    "rootDir": "src",
    "composite": true,
    "strict": true,
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true
  }
}

Create source code directories:

mkdir src && mkdir src/calc

Add source code.

touch src/calc/index.ts src/index.ts

src/calc/index.ts:

export const add = (x: number, y: number) => {
  return x + y;
}

src/index.ts:

export * from './calc';

From this point, we're ready to reuse our library.

Library installation

Create a demo project:

mkdir demo-app && cd demo-app

Init npm:

npm init --yes

Install typescript as a dev dependency:

npm install typescript --save-dev

Update package.json to the following:

{
  "name": "demo-app",
  "version": "1.0.0",
  "description": "A demo project.",
  "main": "index.js",
  "scripts": {
    "build": "tsc --build .",
    "start": "npm run build && node ./dist/index.js"
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}

Init typescript project:

npx tsc --init

Update tsconfig.json to the following:

{
  "compilerOptions": {
    "baseUrl": "./",
    "target": "ES2020",
    "module": "commonjs",
    "strict": true,
    "esModuleInterop": true,
    "outDir": "dist",
    "forceConsistentCasingInFileNames": true
  },
  "references": [
    { "path": "../lib-app/" }
  ]
}

Notice that we've added the reference property, which refers to our library.

Add file src/index.ts:

import { add } from '../../lib-app';

console.log(add(1,3));

Now we can run the project:

npm run start

You also can publish the typescript library to npm. More information is here.