Answer 1

Array.prototype.flat= function() {
    return [].concat(...this.map(item => (Array.isArray(item) ? item.flat() : [item])));
}

Array.prototype.unique = function() {
    return [...new Set(this)]
}

const sort = (a, b) => a - b;

console.log(arr.flat().unique().sort(sort)); // [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 ]

Answer 2

const max = Math.pow(2, 31) - 1;
const min = -Math.pow(2, 31);

const reverseNum = function(x) {

    var y = 0;
    while(x !== 0) {
        y = 10 * y + x % 10;
        x = ~~(x/10);
    }
    if (y > max) return 0;
    if (y < min) return 0;
    return y;
};