array vs array like hash.js

/*
  Traditionally in js we separate arrays and hashes(maps, Object, dictionary, ...)
  Test shows that modern engines havent array optimization - it just hash with automatic <.length> property and sugar array like methods :(

*/

var m = 1000;

var _fill = function(a)
{
  var i = a.length; while(i--)
    a[i] = 0;
};

var filledArray = new Array(m)
var filledHash = {length: m};

_fill(filledArray);
_fill(filledHash);

var _traverse = function(n, a)
{
  var i = n; while(i--)
  {
    var j = a.length; while(j--)
    {
      a[j] |= a[j];
    }    
  }    
};
_speedTest(
  [
    function(n)
    {
      _traverse(n, filledArray);
    },
    function(n)
    {
      _traverse(n, filledHash);
    }
  ],
  10000
);

/*
ie7 10000/10
0: 2373 ms
1: 2314 ms

chrome7
0: 855 ms
1: 818 ms

opera10.62
0: 739 ms
1: 733 ms

ff3.6 1000/5
0: 1468 ms
1: 1501 ms

ff4b3 1000/5
0: 1215 ms
1: 1183 ms
*/