Summary of several methods to use JS to identify browser type and IE version_javascript skills

var isIE=!!window.ActiveXObject;
var isIE6= isIE&&!window.XMLHttpRequest;
var isIE8=isIE&&!!document.documentMode;
var isIE7=isIE&&!isIE6&&!isIE8;
if (isIE){
if (isIE6){
alert("ie6");
}else if (isIE8){
alert("ie8");
}else if (isIE7){
alert("ie7");
}
}

if(navigator.appName == "Microsoft Internet Explorer" && navigator.appVersion.match (/6./i)=="6."){
alert("IE 6");
}
else if(navigator.appName == "Microsoft Internet Explorer" && navigator.appVersion .match(/7./i)=="7."){
alert("IE 7");
}
else if(navigator.appName == "Microsoft Internet Explorer" && navigator .appVersion.match(/8./i)=="8."){
alert("IE 8");
}
else if(navigator.appName == "Microsoft Internet Explorer" && navigator.appVersion.match(/9./i)=="9."){
alert("IE 9");
}

if(navigator.userAgent.indexOf("Opera") != -1) {
alert('Opera');
}
else if (navigator.userAgent.indexOf("MSIE") != -1) {
alert('Internet Explorer');
}
else if(navigator.userAgent.indexOf("Firefox") != -1) {
alert('Firefox');
}
else if(navigator.userAgent.indexOf("Netscape") != -1) {
alert('Netscape');
}
else if(navigator.userAgent.indexOf("Safari") != -1) {
alert('Safari');
}
else{
alert( 'Unrecognized browser. ');
}

if(! 'v1' && !'1'[0 ]){
alert("ie6 or ie7")
}