Michele Nasti

Thoughts on what I learn

Node useful libraries - manage command line arguments with YARGS

When dealing with command line arguments in NodeJS we all know that we have to enquire process.argv object.

This object contains all the strings that compose our nodejs app, so for example

$ node bank.js balance 

can be read inside bank.js as:

/* outputs:

That's a simple case, and we know that process.argv[2] will contain the "command" provided to our script, bank.js (that is also process.argv[1]).

But what if we want to accept parameters like:

$ node bank.js sendMoney --recipient="James" 

or this:

$ node bank.js sendMoney --recipient "James Woods" 

Well, now the problem is becoming a bit more complex, expecially if we want to handle everything with process.argv. Maybe if there's a library that handles all of this...

YARGS: the module that handles command line parameters

YARGS is a npm module that will transform your process.argv into a javascript object. It will handle all the special cases, spaces, quotes, arguments, for you.

Yargs is completely configurable, but its defaults are the best choice for you and your users.

First, let's install this module and save it in our current project:

$ npm i -s yargs 

To use yargs you only have two steps to do:

const yargs = require('yargs');
const argv = yargs.argv;

Now we have an object argv with all the properties set to the command line.

Let's do a quick example:

$ node bank.js sendMoney --recipient "James Woods" 

process.argv will show this:

/* prints:
[ '/usr/local/bin/node',
'James Woods' ]

While YARGS will return this:

/* prints:
{ _: [ 'sendMoney' ],
recipient: 'James Woods',
'$0': 'bank.js' }

As you can see, now we have a Javascript obect with some properties that resamble what we have passed on the command line.

  • argv._ contains the program commands, like balance, sendMoney, etc.
  • argv.recipient contains the property associated with --recipient="James Woods". Note: you can also use spaces, or remove the quotes in case of a single word... Yargs will contain this for you.
  • argv.$0 contains the name of the js file, in case you need it.

Easy, isn't it?

Now you are ready to write your beautiful command line app and be super productive !