阻止冒泡

var btn = document.getElementById('btn');

var div = document.getElementById('div');

btn.onclick = function(ev){

var oEvent = ev||event;

oEvent.cancelBubble = true; //阻止继续向 document 冒泡

div.style.display = 'block';

}

document.onclick = function(){

div.style.display = 'none';

}