How to read command-line arguments in Node.js

Short answer

process.argv is an array: the path to node, the path to the script, and then your arguments. Skip the first two. For the command node app.js input.txt:

const args = process.argv.slice(2);
 
console.log(args);
console.log('file:', args[0]);

Output:

[ 'input.txt' ]
file: input.txt

Options

parseArgs() from node:util understands options like --verbose and --out=report.txt:

import { parseArgs } from 'node:util';
 
const { values, positionals } = parseArgs({
  args: ['input.txt', '--out=report.txt', '--verbose'],
  options: {
    out: { type: 'string', default: 'result.txt' },
    verbose: { type: 'boolean', short: 'v' },
  },
  allowPositionals: true,
});
 
console.log(positionals, values.out, values.verbose);

Output:

[ 'input.txt' ] report.txt true

Without the args option, parseArgs() reads the real process.argv. Here the arguments are passed explicitly to show the result.

Common mistake

All arguments are strings, even numbers. And if the user did not pass an argument, it is undefined, so check it:

const count = process.argv[3];
 
if (count === undefined) {
  console.log('Usage: node app.js <file> <count>');
} else {
  console.log(Number(count) + 1);
}

Output:

Usage: node app.js <file> <count>

Thanks for reading!

Short answer

Options

Common mistake

Functions used in this recipe

Thanks for reading!