SOURCE

function sort(nums){
    if(nums.length < 2) return nums;
    let mid = Math.floor(nums.length / 2);
    let left = [], right = [];
    let temp = nums.splice(mid, 1)[0];
    for(let i = 0; i < nums.length; i++){
        if(nums[i] < temp){
            left.push(nums[i]);
        }else{
            right.push(nums[i])
        }
    }
    return sort(left).concat([temp], sort(right));
}
nums = [5,2,6,7,3,5,1];

console.log(sort(nums))