hash traversal.js

/* 
  es5 introduces new Object api. Object.keys returns array of own enumerable keys of object.
  In es3 we have classic construction "for in hasOwnProperty" for this purposes.
  Test try to find what is best - es3 enumeration or es5
  In es5 we have overhead of array making and allocation
  In es3 we have overhead of enumeration extra properties from prototype chain and filter it(using hasOwnProperty - extra function call) 

  update 1
  according brilliant idea of @abozhilov (http://twitter.com/abozhilov/status/26758011447) there is 3rd way which
  uses nonstandard __proto__ (presents in v8 and JagerMonkey)
*/

var m = 10;
var prefix = '';

var _fill = function(a, len)
{
  var i = len; while(i--)
    a[prefix + i] = 0;
    
  return a;  
};

var aL = _fill({}, m);

_speedTest(
  [
    function(n)
    {
      var a = aL;
      var i = n; while(i--)
      {
        for(var j in a)
        {
          if(a.hasOwnProperty(j))
            ++a[j];
        }
      }
    },
    function(n)
    {
      var a = aL;
      var i = n; while(i--)
      {
        var keys = Object.keys(a);
        
        var j = keys.length; while(j--)
        {
          ++a[keys[j]];
        }
      }
    },
    function(n)
    {
      var a = aL;
      var i = n; while(i--)
      {
        var proto = a.__proto__;
        
        a.__proto__ = null;
        
        for(var j in a)
        {
          ++a[j];
        }
        
        a.__proto__ = proto;
      }
    }
  ],
  100000
);

/*
chrome7 100000
m = 10 prefix = ''
0: 1210 ms
1: 615 ms
2: 936 ms

m = 10 prefix = 'xxx'
0: 1315 ms
1: 837 ms
2: 1327 ms

ff4b3 100000
m = 10 prefix = 'xxx'
0: 1130 ms
1: 1522 ms
2: 496 ms

m = 10 prefix = ''
0: 1215 ms
1: 1375 ms
2: 523 ms
*/

/*
  Conclusion
  
    1) in v8 es5 way is best, in JagerMonkey es3 is best, other engines hasnt Object.keys
    2) v8 have optimization by numeric property names (see difference between cases with prefix = 'xxx' and prefix = '')
    
  update 1
    __proto__ method in JagerMonkey is best

*/