Combinations & Permutations in JS

combinatorics.js

let numbers = '1 2 3'.split(' ').map(n => +n);

getCombinations([], numbers, x => console.log('C', x.join(' ')));
getPermutations([], numbers, x => console.log('P', x.join(' ')));

function getCombinations(first, chars, cb) {
    for (var i = 0; i < chars.length; i++) {
        cb(first.concat(chars[i]));
        getCombinations(first.concat(chars[i]), chars.slice(i + 1), cb);
    }
}

function getPermutations(first, chars, cb) {
    for (var i = 0; i < chars.length; i++) {
        cb(first.concat(chars[i]));
        getPermutations(first.concat(chars[i]), chars.slice(0, i).concat(chars.slice(i + 1)), cb);
    }
}