Creating an npm package

initial files and folders

1. Create a new package project in a new folder npm init -y
2. Create an src folder and a index.ts file inside it.

Running Typescript in Node.js while developing the package

We will start by installing tsx. It uses esbuild to run typescript files on the fly in node.js with zero configuration.

1. run npm install -D tsx

2. add a dev script to package.json to run tsx in watch mode.

   "scripts": {
       "dev": "tsx watch ./src/index.ts",
   }

3. Write some typescript code in index.ts and run npm run dev to see it in action.

Building the package

While esbuild is orders-of-magnitude faster then tsc it doesn't type-check our code. Although there are configuration options to use tsc only for type-checking in tandam with esbuild for the actual compilation, I want to keep our config simple and not rely too much on esbuild other then spontanious zero-config development. So let's use tsc to build our package for production.

1. install the following dev dependencies

   1. typescript - the tsc compiler for our build step
   2. @types/node - types for node.js
   3. rimraf - a rm -rf util for node.js that works on windows too

2. Add a tsconfig.json file to the root of the project with the following code. If you're curious about the configuration options, you can read about them here, or run tsc --init to generate a tsconfig.json file with comments explaining each option...

   {
       "compilerOptions": {
           "target": "esnext",
           "module": "esnext",
           "outDir": "dist",
           "rootDir": "src",
           "strict": true,
           "noEmitOnError": true,
           "moduleResolution": "node",
           "esModuleInterop": true,
           "skipLibCheck": true,
           "forceConsistentCasingInFileNames": true
       },
       "exclude": ["**/*.spec.ts"]
   }

3. Add a build script to package.json to run tsc .

   "scripts": {
       "build": "rimraf dist && tsc",
   }

unit tests and code coverage

1. We'll use vitest - a lightweight next generation drop-in replacement for jest