$document.on("mouseenter mouseleave",".class",function(event){
if(event.type == "mouseover"){
}else if(event.type == "mouseout"){
};
});
mouseenter mouseleave 只有在鼠标指针穿过(离开)被选元素时,才会触发
mouseover mouseout 鼠标指针穿过(离开)被选元素或其子元素,都会触发 (可能会触发多次)