js window.performence

참고

• A better timer for JavaScript

window.performance = window.performance || {};
performance.now = (function() {
  return performance.now       ||
         performance.mozNow    ||
         performance.msNow     ||
         performance.oNow      ||
         performance.webkitNow ||
         function() { return new Date().getTime(); };
})();

javascript profile 역시 모르면 손발이 고생이다.