Merge sort in JS: just keeping fresh with my CS stuff and doing it in JS for fun. So far thsi is memory optimized with merge only being created once just need to do it in-place and it should be even better.

MergeSort

var unsorted = [3, 6, 4, 5, 8, 1, 7, 9, 2];

var mergeSort = (function(){
    var sort = function (toSort) {
        var arlength = toSort.length;
        var midpoint = Math.round(arlength / 2);
        
        if (toSort.length > 1) {
            // better to not slice here since it creates new arrays
            return merge(mergeSort(toSort.slice(0, midpoint)),
                mergeSort(toSort.slice(midpoint, arlength)));
        }
        return toSort;
    };

    // only want one copy of it
    var merge = function (sortedA, sortedB) {
        var toReturn = [];
        var itA = 0, itB = 0, 
            Alength = sortedA.length, Blength = sortedB.length;
        while(itA < Alength && itB < Blength) {
            if (sortedB[itB] < sortedA[itA]) {
                toReturn.push(sortedB[itB++]);
            } else {
                toReturn.push(sortedA[itA++]);
            }
        }
        toReturn = toReturn.concat(sortedB.slice(itB)).concat(sortedA.slice(itA));
        return toReturn;
    };    
   return sort;
})();

console.log(mergeSort(unsorted));