qsort.js

var qsort = function(arr) {
    let partition = function(lidx, ridx) {
        let pval = arr[lidx]    // note: ! may be chosen differently

        let l = lidx - 1
        let r = ridx + 1

        //   >>>>>>> move L towards end 
        // [ lesser, lesser, L, ?, ?, ?, ... (piv) ... , ?, ?, ?, R, greater, greater ]
        //                                               <<<<<<< move R to start
        //  while maintaining (L < piv < R) true. this goes for only that long...  
        //  then swap L & R and try some more until L & R eventually meet into P
        //
        //  P is now the pivot position and all elems of the range hold Ai < pval < Aj 

        do {
            do {                // move L towards end 
                l = l + 1
            } while (arr[l] < pval)

            do  {               // move R towards 
                r = r - 1
            } while (arr[r] > pval)

            if (l >= r) {
                return r
            }

            [arr[l], arr[r]] = [arr[r], arr[l]] // a.k.a. swap
        } while (42)
    }

    let rec = function (lidx, ridx) {
        if (lidx < ridx) {
            let pidx = partition(lidx, ridx)
            let lsort = rec(lidx, pidx)
            let rsort = rec(pidx + 1, ridx)
        }
    }

    rec(0, arr.length - 1)

    return arr
}

console.log(
  qsort(
    [1, 2, 5, 11, 8, 6, 3]))