Merge sort in javascript

Merge sort in javascript

function mergeSort(arr)
{
    if (arr.length < 2){
      return arr;
    }

    var middle = parseInt(arr.length / 2);
    var left   = arr.slice(0, middle);
    var right  = arr.slice(middle, arr.length);

    return merge(mergeSort(left), mergeSort(right));
}

function merge(left, right)
{
    var result = [];
    while (left.length && right.length) {
        if (left[0] <= right[0]) {
            result.push(left.shift());
        } else {
            result.push(right.shift());
        }
    }

    while (left.length){
        result.push(left.shift());
    }

    while (right.length){
        result.push(right.shift());
    }

    console.log(result);

    return result;
}

var a = [34, 203, 3, 746, 200, 984, 198, 764, 9];
console.log(mergeSort(a))