How do I pass command line arguments to a Node.js program?

Question

I have a web server written in Node.js and I would like to launch with a specific folder. I\'m not sure how to access arguments in JavaScript. I\'m running node like this:

Answer 1

No Libs with Flags Formatted into a Simple Object

function getArgs () {
    const args = {};
    process.argv
        .slice(2, process.argv.length)
        .forEach( arg => {
        // long arg
        if (arg.slice(0,2) === '--') {
            const longArg = arg.split('=');
            const longArgFlag = longArg[0].slice(2,longArg[0].length);
            const longArgValue = longArg.length > 1 ? longArg[1] : true;
            args[longArgFlag] = longArgValue;
        }
        // flags
        else if (arg[0] === '-') {
            const flags = arg.slice(1,arg.length).split('');
            flags.forEach(flag => {
            args[flag] = true;
            });
        }
    });
    return args;
}
const args = getArgs();
console.log(args);

Examples

Simple

input

node test.js -D --name=Hello

output

{ D: true, name: 'Hello' }

Real World

input

node config/build.js -lHRs --ip=$HOST --port=$PORT --env=dev

output

{ 
  l: true,
  H: true,
  R: true,
  s: true,
  ip: '127.0.0.1',
  port: '8080',
  env: 'dev'
}

Answer 2

Passing arguments is easy, and receiving them is just a matter of reading the process.argv array Node makes accessible from everywhere, basically. But you're sure to want to read them as key/value pairs, so you'll need a piece to script to interpret it.

Joseph Merdrignac posted a beautiful one using reduce, but it relied on a key=value syntax instead of -k value and --key value. I rewrote it much uglier and longer to use that second standard, and I'll post it as an answer because it wouldn't fit as a commentary. But it does get the job done.

   const args = process.argv.slice(2).reduce((acc,arg,cur,arr)=>{
     if(arg.match(/^--/)){
       acc[arg.substring(2)] = true
       acc['_lastkey'] = arg.substring(2)
     } else
     if(arg.match(/^-[^-]/)){
       for(key of arg.substring(1).split('')){
         acc[key] = true
         acc['_lastkey'] = key
       }
     } else
       if(acc['_lastkey']){
         acc[acc['_lastkey']] = arg
         delete acc['_lastkey']
       } else
         acc[arg] = true
     if(cur==arr.length-1)
       delete acc['_lastkey']
     return acc
   },{})

With this code a command node script.js alpha beta -charlie delta --echo foxtrot would give you the following object

args = {
 "alpha":true,
 "beta":true,
 "c":true,
 "h":true,
 "a":true,
 "r":true
 "l":true,
 "i":true,
 "e":"delta",
 "echo":"foxtrot"
}

Answer 3

Standard Method (no library)

The arguments are stored in process.argv

Here are the node docs on handling command line args:

process.argv is an array containing the command line arguments. The first element will be 'node', the second element will be the name of the JavaScript file. The next elements will be any additional command line arguments.

// print process.argv
process.argv.forEach(function (val, index, array) {
  console.log(index + ': ' + val);
});

This will generate:

$ node process-2.js one two=three four
0: node
1: /Users/mjr/work/node/process-2.js
2: one
3: two=three
4: four

Answer 4

2018 answer based on current trends in the wild:

---

Vanilla javascript argument parsing:

const args = process.argv;
console.log(args);

This returns:

$ node server.js one two=three four
['node', '/home/server.js', 'one', 'two=three', 'four']

Official docs

---

Most used NPM packages for argument parsing:

Minimist: For minimal argument parsing.

Commander.js: Most adopted module for argument parsing.

Meow: Lighter alternative to Commander.js

Yargs: More sophisticated argument parsing (heavy).

Vorpal.js: Mature / interactive command-line applications with argument parsing.

Answer 5

Here's my 0-dep solution for named arguments:

const args = process.argv
    .slice(2)
    .map(arg => arg.split('='))
    .reduce((args, [value, key]) => {
        args[value] = key;
        return args;
    }, {});

console.log(args.foo)
console.log(args.fizz)

Example:

$ node test.js foo=bar fizz=buzz
bar
buzz

Note: Naturally this will fail when the argument contains a =. This is only for very simple usage.

Answer 6

You can reach command line arguments using system.args. And i use the solution below to parse arguments into an object, so i can get which one i want by name.

var system = require('system');

var args = {};
system.args.map(function(x){return x.split("=")})
    .map(function(y){args[y[0]]=y[1]});

now you don't need to know the index of the argument. use it like args.whatever

Note: you should use named arguments like file.js x=1 y=2 to use this solution.