npx is an useful tool to run one-off commands like create-react-app, http-server etc.

In this post I’ll go through the steps needed to create a command line tool that can be invoked using npx.

Let’s start with a simple hello world script

console.log("hello world");

This prints “hello world” when you run it

$ node index.js
hello world

To make this runnable by npx, we need to convert this into an executable file by adding the node shebang line

#!/usr/bin/env node

console.log("hello world");

Let’s then create a npm package so this file can be published to npm

$ npm init -y

This will create the package.json file.

If you publish this package now, it can be installed by others but they won’t be able to execute it using npx. For this we need to reference this file in the bin field of package.json

{
  "name": "npx-example",
  "version": "1.0.0",
  "main": "index.js",
  "bin": "index.js",
  "scripts": {
    "start": "node ."
  },
  "license": "MIT"
}

You can now publish this package

$ npm publish

You can find a complete example in this repo.