js 不用重复检测浏览器提高效率

// 方式1
function addevent(el, type, fn){
if(el.addeventlistener){
el.addeventlistener(type, fn, false);
}else{
el.attachevent('on'+type, fn)
}
}

// 方式2
var addevent = document.addeventlistener ?
function(el, type, fn) {el.addeventlistener(type, fn, false);} :
function(el, type, fn) {el.attachevent('on'+type, fn)};