collatz conjecture

collatz.js

#!/usr/bin/env node
'use strict';

const range = function(start, stop) {
    return Array.apply(null, { length: 1 + stop - start })
        .map((v, i) => start + i);
};

const collatz = function(n, len) {
    let steps = [];
    while(n != 1) {
        // if n is even, divide by 2
        // if n is odd, multiply by 3 and add 1
        n = (n % 2 === 0)
            ? n / 2
            : 3 * n + 1;
        steps.push(n);
    }
    return (typeof len === 'undefined')
        ? steps
        : steps.length;
}

// console.log(range(1, 100).map( e => collatz(e)));
// module.exports = {'range': range, 'collatz': collatz};