Xns NPM | npm.io

xns

Turn any function into a script that can be invoked from the command line.

xns stands for eXecute Node Script!

Problem

Let's say you have written a cool JavaScript (or TypeScript) function!

get-bitcoin-price.ts:

import got from 'got';

export default async (): Promise<string> => {
  const res = await got('https://api.coinbase.com/v2/prices/spot');
  const {currency, amount} = JSON.parse(res.body).data;
  return `1 Bitcoin is worth ${currency} ${amount}`;
};

Now you would like to execute this function in your terminal. Current options are not ideal:

You could make the function self-invoking, but then it also executes by itself as soon as it's imported somewhere else.
You could make another file, import the function and execute it, then run that file, but it's cumbersome.

Solution

Wrap your function in xns():

get-bitcoin-price.ts:

import xns from 'xns';
import got from 'got';

export default xns(async (): Promise<string> => {
  const res = await got('https://api.coinbase.com/v2/prices/spot');
  const {currency, amount} = JSON.parse(res.body).data;
  return `1 Bitcoin is worth ${currency} ${amount}`;
});

Now you can execute the function from your terminal:

ts-node get-bitcoin-price
1 Bitcoin is worth USD 7767.655

You can also still import the function from somewhere else as usual and it will not execute itself 👌

Why `xns`?

Works with node and transpiled languages: ts-node, babel-node...
Can still be imported as normal
Prints out the return value
Fully typed, keep Typescript typings
Wrapping function in xns does not change behavior of your app
Exit code 1 on error, exit code 0 on success, perfect for CRON jobs
No Unhandled promise rejection errors, proper catch handler built in
Works with synchronous and asynchronous functions
Works with ES Modules and CommonJS import style
- Use named export for CommonJS: const {xns} = require('xns')

Old version of `xns`

This is version 2 of xns. Version 1 worked completely different, it compiled a file using babel and called the default export. It's still supported if you have Babel. See here for the old API.