basic quicksort implementation in JavaScript

quicksort.js

function qs(arr, lf = 0, rt) {
    function swap(ix1, ix2){
        var temp = arr[ix1]
        arr[ix1] = arr[ix2]
        arr[ix2] = temp
    }

    rt = rt || arr.length - 1;

    if (rt - lf === 1) {
        if (arr[rt] < arr[lf]) {
            swap(rt, lf)
        }

        return arr
    }

    var pvt = arr[Math.round((lf + rt) / 2)];
    
    for(var i = lf, j = rt; i <= j;) {
        for (;pvt > arr[i];){
            i++
        }
        
        for (;pvt < arr[j];){
            j--
        }

        if (i <= j) {
            swap(i, j);
            i++;
            j--;
        }
    }

    if (lf < i - 1) {
        qs(arr, lf, i - 1)
    }

    if (rt > i) {
        qs(arr, i, rt)
    }


    return arr
    
}