1. 判断是否存在于
   

   var a = "b" in c;

2. 字符串转数组新写法
   

   var split = "split",
   	S = " ",
       events = "click dblclick mousedown mousemove mouseout mouseover mouseup touchstart touchmove touchend touchcancel"[split](S);

var h = 2;
h = ~~h;
//怎么理解？