浏览器判断一览表
{ ie : !!window.ActiveXObject, ie6 : document.all && !window.XMLHttpRequest, ie7 : document.all && window.XMLHttpRequest && !document.querySelector, ie8 : document.all && document.querySelector && !document.addEventListener, ie9 : document.all && document.addEventListener && !window.atob, ie10 : document.all && window.atob, ie11 : '-ms-scroll-limit' in document.documentElement.style && '-ms-ime-align' in document.documentElement.style, chrome : !!window.chrome && window.chrome.webstore, firefox : !!window.sidebar, safari : /constructor/i.test(window.HTMLElement), opera : !!window.opera || /opera|opr/i.test(navigator.userAgent) }