refer to : http://mir.aculo.us/2009/11/08/6-easy-things-you-can-do-to-improve-your-javascript-runtime-performance/
#1 avoid function calls
#2 embrace the language: []>array, {} > object
#3 loop: no loop > loop
#4 cache globals: function(){var w =window;}
#5 expression tuning: false move to before &&, true move to before ||
#6 what not to use: e.g. with , eval, try catch,