添加事件监听器和移除 封装
function addEvent(domobj, type, fn) {
if(domobj.addEventListener) {
domobj.addEventListener(type, fn);//现代浏览器支持,IE低版不支持
} else {
domobj.attachEvent("on" + type, fn);//IE低版支持
}
}
function removeEvent() {
if(domobj.removeEventListener) {
domobj.removeEventListener(type, fn);
} else {
domobj.detachEvent("on" + type, fn);
}
}