Command-line arguments in Node.js

When working with Node.js scripts, you might need to access the command-line arguments passed to the script. This can be useful for configuring the script or passing additional information to it. But how can you do that?

The process.argv array

Node.js provides the process.argv array, which contains the command-line arguments passed to the Node.js process. The first two elements of the array are the path of the Node.js executable and the file being executed. Let's look at an example to make it clearer:

// $ node my-script.js --name=John --age=30

process.argv;
/* [
  '/path/to/node',
  '/path/to/my-script.js',
  '--name=John',
  '--age=30'
] */

Extracting command-line arguments

In order to get only the command-line arguments passed to the script, you can use Array.prototype.slice() to remove the first two elements of the process.argv array. Then, you can use them as needed in your script.

const getCmdArgs = () => process.argv.slice(2);

// $ node my-script.js --name=John --age=30
getCmdArgs(); // ['--name=John', '--age=30']

Checking if a flag is present

If you need to check if a specific flag is present in the command-line arguments, you can use Array.prototype.every() and Array.prototype.includes() to check if process.argv contains the specified flag. Then, you can use a regular expression to test if the specified flag is prefixed with - or -- and prefix it accordingly.

const hasFlags = (...flags) =>
  flags.every(flag =>
    process.argv.includes(/^-{1,2}/.test(flag) ? flag : '--' + flag)
  );

// node my-script.js -s --test --cool=true
hasFlags('-s'); // true
hasFlags('--test', 'cool=true', '-s'); // true
hasFlags('special'); // false