JS判断浏览器

if (window.XMLHttpRequest) { //Mozilla, Safari,IE7 
    alert('Mozilla, Safari,IE7 ');
    if (!window.ActiveXObject) { // Mozilla, Safari,
        alert('Mozilla, Safari');
    } else {
        alert('IE7');
    }
} else {
    alert('IE6');
}

写法二：

if (window.XMLHttpRequest) //判断浏览器是否属于Mozilla,Sofari
{
    alert("firefox");
} else if (window.ActiveXObject) //判断浏览器是否属于IE
{
    var browser = navigator.appName
    var b_version = navigator.appVersion
    var version = b_version.split(";");
    var trim_Version = version[1].replace(/[ ]/g, "");
    if (browser == "Microsoft Internet Explorer" && trim_Version == "MSIE7.0") {
        alert("IE 7.0");
    } else if (browser == "Microsoft Internet Explorer" && trim_Version == "MSIE6.0") {
        alert("IE 6.0");
    }
}