js 判断ie

var isIE = !!window.ActiveXObject;
    var isIE6 = isIE && !window.XMLHttpRequest;
    var isIE7 = !!(!window.addEventListener && window.XMLHttpRequest && !document.querySelectorAll);
    var isIE8 = !!(!window.addEventListener && document.querySelectorAll);
    $(function(){
        if(isIE || isIE6 || isIE7 || isIE8){
           //do something
        }else{
           //do something
        }
    })