http://zxhfighter.github.io/blog/javascript/2013/03/15/javascript-quiz-remark.html
http://www.ruanyifeng.com/blog/2011/06/10_design_defects_in_javascript.html
http://blog.lyuehh.com/javascript/2013/12/29/javascript-note-part3.html
http://www.nczonline.net/blog/2010/02/16/my-javascript-quiz/#comment-4568