Function merge

javascript/0912-sort-an-array.js:21–52

(left, right, mid, nums)

};

const merge = (left, right, mid, nums) => {
    const arr1 = nums.slice(left, mid + 1);
    const arr2 = nums.slice(mid + 1, right + 1);

    let p1 = 0;
    let p2 = 0;
    let gp = left;

    while (p1 < arr1.length && p2 < arr2.length) {
        if (arr1[p1] < arr2[p2]) {
            nums[gp] = arr1[p1];
            p1++;
        } else {
            nums[gp] = arr2[p2];
            p2++;
        }
        gp++;
    }

    while (p1 < arr1.length) {
        nums[gp] = arr1[p1];
        p1++;
        gp++;
    }

    while (p2 < arr2.length) {
        nums[gp] = arr2[p2];
        p2++;
        gp++;
    }
    return nums;
};