CLI apps in TypeScript via ts-node

I really like the ts-node project. It allows you to run TypeScript in Node.js directly, without having to run the files through the TypeScript compiler (tsc), first. It does this by registering a handler for files with the .ts or .tsx file extentions and relying upon ts-node to marshall back and forth to the TypeScript compiler, on the fly. It also supports a TypeScript REPL which is really neat.

I’ve mainly been using it for unit tests in Node projects (example) to avoid having an intermediate build step. Also, increasingly, I’ve been using it to execute TypeScript directly on some of my own server-side projects at runtime. Again, doing this reduces a build-time step and reduces friction.

Lately, I’ve been using Node more and more to write CLI apps and thought it would be neat if ts-node could be used for this as well. It turns out it’s pretty easy.

First, install ts-node:

npm install ts-node

Then, create your TypeScript module file that will contain your CLI logic.

cli.ts

export function run() {
  const message: string = "Hello from TypeScript!";
  console.log(message);
}

Now, create your entry script. This is the script you will run from your shell.

my-script

#!/usr/bin/env node

require('ts-node').register();
require('./cli.ts').run();

You need to make this file executable first, so run chmod +x ./my-script.

Now, you can run ./my-script from your shell:

> ./my-script
Hello from TypeScript!

If you make changes to the cli.ts file, they will be picked up the next time you run my-script because the latest is running through ts-node.