QuickSelect median of medians.js

function partition(arr, left, right, pivot) {
    var temp = arr[pivot];
    arr[pivot] = arr[right];
    arr[right] = temp;
    var track = left;
    for (var i = left; i < right; i++) {
        if (arr[i]<arr[right]) {
            var t = arr[i];
            arr[i] = arr[track];
            arr[track] = t;
            track++;
        }
    }
    temp = arr[track];
    arr[track] = arr[right];
    arr[right] = temp;
    return track;
}



function selectIdx(arr, left, right, k) {
    if (left == right) {
        return arr[left];
    }
    var dest = left + k;
    while (true) {
        var pivotIndex = right - left + 1 <=5?Math.floor(Math.random()*(right-left+1))+left: medianOfMedians(arr,left,right);
        pivotIndex = partition(arr, left, right, pivotIndex);
        if (pivotIndex == dest)
            return pivotIndex;
        else if (pivotIndex<dest) {
            left = pivotIndex + 1;
        } else {
            right =  pivotIndex -1;
        }
    }
}



function medianOfMedians(arr,left,right) {
    var numMedians = Math.ceil((right-left)/5);
    for (var i = 0 ; i < numMedians; i++) {
        var subLeft = left + i*5;
        var subRight = subLeft + 4;
        if (subRight > right)  {
            subRight = right;
        }
        var medianIdx = selectIdx(arr, subLeft, subRight, Math.floor((subRight-subLeft)/2));
        var temp = arr[medianIdx];
        arr[medianIdx] = arr[left+i];
        arr[left+i] = temp;
    }
    return selectIdx(arr, left, left + numMedians -1, Math.floor(numMedians/2));

}

function selectK(arr, k) {
    if (!Array.isArray(arr) || arr.length == 0 || arr.length-1 < k) {
        return;
    }
    var idx = selectIdx(arr,0,arr.length -1,k);
    return arr[idx];

}

Is line 24 a mistake?
Should be:

        return left;