IE瀏覽器版本的判斷

   var userAgent = navigator.userAgent; //取得瀏覽器的userAgent字串  
            var isIE = userAgent.indexOf("compatible") > -1 && userAgent.indexOf("MSIE") > -1; //判斷是否IE<11瀏覽器   
            var isEdge = userAgent.indexOf("Windows NT 6.1") > -1 && !isIE; //判斷是否IE的Edge瀏覽器
            var isIE11 = userAgent.indexOf(`Trident`) > -1 && userAgent.indexOf("rv:11.0") > -1;
            if (isIE) {
                var reIE = new RegExp("MSIE (\d+\.\d+);");
                reIE.test(userAgent);
                var fIEVersion = parseFloat(RegExp["$1"]);
                if (fIEVersion == 7) {
                    return 7;
                } else if (fIEVersion == 8) {
                    return 8;
                } else if (fIEVersion == 9) {
                    return 9;
                } else if (fIEVersion == 10) {
                    return 10;
                } else {
                    return 6;//IE版本<=7
                }
            } else if (isEdge) {
                return `edge`;//edge
            } else if (isIE11) {
                return 11; //IE11  
            } else {
                return -1;//不是ie瀏覽器
            }