对Event事件进行兼容性处理

var EventUtil = {
			getTarget:function (event) {
				return event.target || event.srcElement	
			},
			preventDefault:function (event) {
			event.preventDefault?event.preventDefault():event.returnValue = false;
		},
		stopPropagation:function (event) {
			event.stopPropagation?event.stopPropagation():event.cancelBubble = true;
		}
	}