经常遇到的js兼容问题

1.	关于使用event对象，
(1)	function(event){
e = ev ||event
}
2.	获取滚动条的兼容
var scrollTop = document.documentElement.scrollTop || document.scrollTop
3.	阻止浏览器默认行为兼容
preventDefault : function(event) {
if(event.preventDefault) {
event.preventDefault()
}else {
event.returnValue = false
}
}

4.	阻止事件冒泡的兼容
stopPropagation : function(event) {
if(event.stopPropagation) {
event.stopPropagation()
}else {
event.canceBubble = true
}
}
5.	document.ondragstart = function(){
			return false;
}