quciksort.js

Array.prototype.swap = function(a, b) { 
  var tmp = this[a]; 
  this[a] = this[b];
  this[b] = tmp;
};

Array.prototype.qsort = function(key) {
  if(key === void 0) {
    key = function(x) {
      return x;
    };
  }
  var findPivot = function(a, left, right) {
    var mid = Math.floor(left + (right-left) / 2)
        pivotIndex = null;
    if(a[left] < a[mid] && a[mid] < a[right]) {
      pivotIndex = mid
    } else if(a[left] < a[right]) {
      pivotIndex = left
    } else {
      pivotIndex = right
    }

    return pivotIndex;
  },
  partition = function(a, l, r, p) {
    var storeIndex = l,
        pivot = key(a[p]);
    a.swap(p, r);
    for(i = l; i <= r - 1; i++) {
      if(key(a[i]) <= pivot) {
        a.swap(i, storeIndex);
        storeIndex = storeIndex + 1;
      }
    }

    a.swap(storeIndex, r);
    return storeIndex;
  },
  qsort = function(l, left, right) {
    if(left < right) {
      var pivotIndex = findPivot(l, left, right);
      var newPivotIndex = partition(l, left, right, pivotIndex);

      qsort(l, left, newPivotIndex - 1);
      qsort(l, newPivotIndex + 1, right);
    }
  };
  qsort(this, 0, this.length - 1);

  return this;
}

var a = [1,4,2,3];
console.log(a);
console.log(a.qsort(function(x) { return x['a'] }));
var b = [{'a': 4}, {'a': 2}, {'a': 3}, {'a': 1}];
console.log(b);
console.log(b.qsort(function(x) { return x[1] }))
var c = [["a", 1], ["b", 2], ["c", 4], ["d", 3]];