mergeSort.js

/**
 * merge sort
 **/


 var arr = [8,7,9,30,13,8,99,124, 5];
 //var arr = [1,10,9];

var newArr = [];
var ii = 0;
function mergeSort(arr, left, right) {
    var resultArr = [];
    var len = right -left;
    if (len === 0) resultArr.push(arr[left]);

    if (len > 0) {
        var mid = Math.floor(len/2, 10) + left;
        var leftArr = mergeSort(arr, left, mid);
        var rightArr = mergeSort(arr, mid + 1, right);
        resultArr = mergeLR(leftArr, rightArr);
    }
    return resultArr;
}

function mergeLR(larr, rarr) {
    var result = [];

    var i = 0, j = 0;
    var llen = larr.length;
    var rlen = rarr.length;
    while (i < llen && j < rlen) {
        if (larr[i] <= rarr[j]) {
            result.push(larr[i]);
            i++;
        } else {
            result.push(rarr[j]);
            j++;
        }
    }

    if (i >= llen) {
        result = result.concat(rarr.slice(j));
    } else {
        result = result.concat(larr.slice(i));
    }
    return result;
}

console.info(mergeSort(arr, 0, arr.length - 1));