Given a positive integer given as a command line argument, determines if that number is prime.

isPrime.js

#!/usr/bin/env node

const process = require('process');
const num = parseInt(process.argv[2], 10);

const CompositeRegex = /^(..+)\1+$/;

function isPrime(num) {
    const str = new Array(num + 1).join(' ');
    return !CompositeRegex.test(str);
}

const prime = isPrime(num);
if (prime) {
    console.log('prime');
} else {
    console.log('not prime');
}