Implementation of Randomized Quick Sort Algorithm

quickSort.js

// Sorts array in ascending order
function quickSort(arr) {
    if (arr == null
        || !Array.isArray(arr)) return;
    mQuickSort(arr, 0, arr.length);

    function mQuickSort(arr, startIdx, endIdx) {
        if (endIdx - startIdx <= 1) return;
        if (endIdx - startIdx == 2 && arr[0] > arr[1]) {
            var t = arr[1];
            arr[1] = arr[0];
            arr[0] = t;
            return;
        }
        var pivotIdx = Math.floor(Math.random() * (endIdx - startIdx)) + startIdx;
        var pivot = arr[pivotIdx];
        arr[pivotIdx] = arr[endIdx - 1];
        arr[endIdx - 1] = pivot;
        var i = startIdx;
        for (var j = startIdx; j < endIdx - 1; j++) {
            if (arr[j] <= pivot) {
                var t = arr[j];
                arr[j] = arr[i];
                arr[i] = t;
                i++;
            }
        }
        arr[endIdx - 1] = arr[i];
        arr[i] = pivot;
        mQuickSort(arr, startIdx, i);
        mQuickSort(arr, i + 1, endIdx);
    }
}