gabswim / inspace

Typescript Node.js based Command Line Interface showing who is in space

Minimal Typescript based Command Line Interface (CLI) with Node.js

Our goal is to create a Node.js based Command Line Interface (CLI) using Typescript. This setup includes top-Level await support and ES module imports.

What We’re Going to Build

For this tutorial, we’re going to create a CLI called inspace. When executed the CLI will output the current people in space.

Getting Started

Create a new directory for the project. Call it whatever you want, I'm using inspace:

mkdir inspace
cd inspace

Setup a new npm package be creating a package.json file:

npm init -y

To support importing ES modules add the type property to the generated package.json file:

{
  "type": "module",
  // rest...
}

To enable executing the CLI add the bin property to the generated package.json file:

{
  "bin": "src/index.ts",
  // rest...
}

Create an tsconfig.json file in the same folder and include the following to enable importing ES modules and include top level await support:

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "ES2022",
    "esModuleInterop": true,
    "moduleResolution": "Node"
  }
}

Creating the Entrypoint

Create the Typescript entrypoint src/index.ts file, to match the package.json bin property. Include the following shebang as the first line of the file:

#!/usr/bin/env npx ts-node --esm

The esm flag is include to support Ensure the file includes execution permission. Execution permission can be added using the following command:

chmod u+x ./src/index.ts

Add Typescript to the file to help test execution:

console.log("Typescript executed successfully");

The file (CLI) can now be executed directly as if it was a binary.

./src/index.ts

Making the Command Available Globally

The npm package can now be locally installed globally using the following command:

npm install -g

After installation the npm package can now be executed using the package name:

inspace

Package Dependencies

The foundation of the CLI has now been setup. The CLI's functionality is ready to be fleshed out and is supplemental to the CLI's foundation. The following dependencies will be added only to showcase example CLI functionality.

• axios - promise based HTTP client
• chalk — colorizes the output
• clear — clears the terminal screen
• figlet — creates ASCII art from text

Install the dependencies using the following command:

npm install -S axios chalk clear figlet

Example CLI Functionality

Add imports for the installed packages to the Typescript entrypoint src/index.ts file.

import axios from 'axios';
import chalk from 'chalk';
import clear from 'clear'
import figlet from 'figlet'

We are using the Open Notify API as a data source. Create types to handle the API response.

type People = {
  name: string;
  craft: string;
}

type Inhabitants = {
  number: number;
  people: People[]
}

Add a function to encapsulate interacting with the Open Notify API using Axios.

async function getInhabitantsOfSpace() {
  const response = await axios.get<Inhabitants>("http://api.open-notify.org/astros.json");
  return response.data;
}

Clear the terminal screen using clear, then print a ASCII header using figlet.

clear();
console.log(chalk.yellowBright(figlet.textSync('InSpace', { horizontalLayout: 'full' })));

Get the inhabitants of space using the getInhabitantsOfSpace function and print the results using chalk.

const inhabitants = await getInhabitantsOfSpace();
console.log(chalk.blue(`There is currently ${inhabitants.number} people in space`));
inhabitants.people.forEach(person => console.log(`${person.name} - ${chalk.yellow(person.craft)}`));

Publishing the CLI to NPM

The npm package can now be published if logged into npm using the following command:

npm publish

The npm package can now be installed globally using the following command:

npm install -g inspace

After installation the npm package can now be executed using the package name:

inspace