v8 loop.js

var sys = require('sys');
var uuid = function() {
  var uuid = '', i;
  for (i = 0; i < 32; i++) {
    uuid += Math.floor(Math.random() * 16).toString(16);
  }
  return uuid;
};

var a = {}, u, index=[];
for( var i = 0; i < 1000000; ++i) {
  u = uuid();
  a[u] = {id: "asdfasdfasda"};
  index[index.length] = u;
}

var start = (new Date).getTime(), key;
for(key in a) {
  a[key];
}
sys.puts("for key in loop: " + ((new Date).getTime() - start));

var start = (new Date).getTime(), keys = Object.keys(a), len = keys.length;
while(--len) {
  a[keys[len]];
}
sys.puts("while loop with keys: " + ((new Date).getTime() - start));

var start = (new Date).getTime(), len = index.length
while(--len) {
  a[index[len]];
}
sys.puts("while loop with index: " + ((new Date).getTime() - start));