https://leetcode.com/problems/reverse-integer/

reverse_an_integer.js

/**
 * @param {number} x
 * @return {number}
 */
var reverse = function(x) {
    let y = 0;
    let num = Math.abs(x);
    const intMax = Math.pow(2, 31) + 1;
    
    while(num != 0) {
        let temp = num % 10; // last digit
        num = Math.floor(num/10); // update x (remove last digit)
        y = (y * 10) + temp;
    }
    if (y > intMax) return 0;
    
    return Math.sign(x) * y;
};