gistfile1.js

var one = {}
  , two = {'o':true}
  ;

function ifTest () {
  var start = new Date();
  var i = 0;
  while (i<10000) {
    if (one.o) true
    if (two.o) true
    i++;
  }
  var end = new Date();
  console.log('ifTest: '+(end - start))
}

function inTest () {
  var start = new Date();
  var i = 0;
  while (i<10000) {
    if ('o' in one) true
    if ('o' in two) true
    i++
  }
  var end = new Date();
  console.log('inTest: '+(end - start))
}

ifTest();
inTest();