SOURCE

/**
 * @param {number} a
 * @param {number} b
 * @return {number}
 */
var getSum = function(a, b) {
    if((a&b) === 0){
        return a ^ b;
    } else {
        return getSum(a ^ b, (a&b)<<1);
    }
};
console.log(getSum(20,30))