SOURCE

var merge = function(nums1, nums2) {
    let re = [];
    let indexL = 0;
    let indexR = 0;
    let m = nums1.length;
    let n = nums2.length
    while(indexL < m && indexR < n) {
        if(nums1[indexL] < nums2[indexR]){
            re.push(nums1[indexL++])
        } else {
            re.push(nums2[indexR++])
        }
    }
    if (indexL < m) {
        re.push(...nums1.slice(indexL));
    }
    if (indexR < n) {
        re.push(...nums2.slice(indexR));
    }
    return re;
};

let a = [1,2,3,4,6];
let b = [2,2,5,7];
console.log(merge(a,b))