Javascript Algorithm Array Sort Merge Sort

function merge(leftA, rightA){
    var results= [], leftIndex= 0, rightIndex= 0;

    while (leftIndex < leftA.length && rightIndex < rightA.length) {
        if( leftA[leftIndex]<rightA[rightIndex] ){
            results.push(leftA[leftIndex++]);
        } else {/*from  www. ja v  a  2  s. co m*/
            results.push(rightA[rightIndex++]);
        }
    }
    var leftRemains = leftA.slice(leftIndex),
        rightRemains = rightA.slice(rightIndex);

    // add remaining to resultant array
    return results.concat(leftRemains).concat(rightRemains);
}

function mergeSort(array) {
    if(array.length<2){
        return array; // Base case: array is now sorted since it's just 1 element
    }

    var midpoint = Math.floor((array.length)/2),
        leftArray = array.slice(0, midpoint),
        rightArray = array.slice(midpoint);

    return merge(mergeSort(leftArray), mergeSort(rightArray));
}
let a = mergeSort([6,1,23,4,2,3]); // [1, 2, 3, 4, 6, 23]
console.log(a);