Function isHappy

javascript/0202-happy-number.js:8–17

(n, seen = new Set())

 * @return {boolean}
 */
var isHappy = (n, seen = new Set()) => {
    const hasCycle = () => n === 1 || seen.has(n);
    while (!hasCycle()) {
        /* Time O(log(N)) */
        seen.add(n); /* Space O(log(N)) */
        n = getNext(n); /* Time O(log(N)) */
    }

    return n === 1;
};

var getNext = (n, sum = 0) => {
    while (0 < n) {