我知道这是一个老问题，但如果有人再次遇到这个问题，并且无法检测IE11，这里有一个适用于所有当前版本的IE的有效解决方案。

var isIE = false;
if (navigator.userAgent.indexOf('MSIE') !== -1 || navigator.appVersion.indexOf('Trident/') > 0) {
    isIE = true;   
}

使用上面的答案;简单压缩返回布尔值:

var isIE = /（MSIE|三叉戟\/|Edge\/）/i.test（navigator.userAgent）;

对于任何版本的Internet Explorer都返回true:

function isIE(userAgent) {
  userAgent = userAgent || navigator.userAgent;
  return userAgent.indexOf("MSIE ") > -1 || userAgent.indexOf("Trident/") > -1 || userAgent.indexOf("Edge/") > -1;
}

userAgent参数是可选的，默认为浏览器的用户代理。

方法1: 美元。浏览器在jQuery 1.3版中已弃用，并在1.9版中被移除

if ( $.browser.msie) {
  alert( "Hello! This is IE." );
}

方法2: 使用条件注释

<!--[if gte IE 8]>
<p>You're using a recent version of Internet Explorer.</p>
<![endif]-->

<!--[if lt IE 7]>
<p>Hm. You should upgrade your copy of Internet Explorer.</p>
<![endif]-->

<![if !IE]>
<p>You're not using Internet Explorer.</p>
<![endif]>

方法03:

 /**
 * Returns the version of Internet Explorer or a -1
 * (indicating the use of another browser).
 */
function getInternetExplorerVersion()
{
    var rv = -1; // Return value assumes failure.

    if (navigator.appName == 'Microsoft Internet Explorer')
    {
        var ua = navigator.userAgent;
        var re  = new RegExp("MSIE ([0-9]{1,}[\.0-9]{0,})");
        if (re.exec(ua) != null)
            rv = parseFloat( RegExp.$1 );
    }

    return rv;
}

function checkVersion()
{
    var msg = "You're not using Internet Explorer.";
    var ver = getInternetExplorerVersion();

    if ( ver > -1 )
    {
        if ( ver >= 8.0 ) 
            msg = "You're using a recent copy of Internet Explorer."
        else
            msg = "You should upgrade your copy of Internet Explorer.";
    }

    alert( msg );
}

方法04: 使用JavaScript/手动检测

/*
     Internet Explorer sniffer code to add class to body tag for IE version.
     Can be removed if your using something like Modernizr.
 */
 var ie = (function ()
 {

     var undef,
     v = 3,
         div = document.createElement('div'),
         all = div.getElementsByTagName('i');

     while (
     div.innerHTML = '<!--[if gt IE ' + (++v) + ']><i></i>< ![endif]-->',
     all[0]);

     //append class to body for use with browser support
     if (v > 4)
     {
         $('body').addClass('ie' + v);
     }

 }());

参考链接

还有另一个简单的(但人类可读的)函数来检测浏览器是否是IE(忽略Edge，它一点都不差):

function isIE() {
  var ua = window.navigator.userAgent;
  var msie = ua.indexOf('MSIE '); // IE 10 or older
  var trident = ua.indexOf('Trident/'); //IE 11

  return (msie > 0 || trident > 0);
}

您可以检测到所有Internet Explorer(最近测试的版本12)。

<script>
    var $userAgent = '';
    if(/MSIE/i['test'](navigator['userAgent'])==true||/rv/i['test'](navigator['userAgent'])==true||/Edge/i['test'](navigator['userAgent'])==true){
       $userAgent='ie';
    } else {
       $userAgent='other';
    }

    alert($userAgent);
</script>

请看这里https://jsfiddle.net/v7npeLwe/