根据微软的说法，以下是最好的解决方案，它也很简单:

function getInternetExplorerVersion()
// Returns the version of Internet Explorer or a -1
// (indicating the use of another browser).
{
    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 );
}

我为此做了一个方便的下划线混合。

_.isIE();        // Any version of IE?
_.isIE(9);       // IE 9?
_.isIE([7,8,9]); // IE 7, 8 or 9?

_.mixin({ isIE: function(mixed) { if (_.isUndefined(mixed)) { mixed = [7, 8, 9, 10, 11]; } else if (_.isNumber(mixed)) { mixed = [mixed]; } for (var j = 0; j < mixed.length; j++) { var re; switch (mixed[j]) { case 11: re = /Trident.*rv\:11\./g; break; case 10: re = /MSIE\s10\./g; break; case 9: re = /MSIE\s9\./g; break; case 8: re = /MSIE\s8\./g; break; case 7: re = /MSIE\s7\./g; break; } if (!!window.navigator.userAgent.match(re)) { return true; } } return false; } }); console.log(_.isIE()); console.log(_.isIE([7, 8, 9])); console.log(_.isIE(11)); <script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js"></script>

你的代码可以做检查，但正如你所认为的，如果有人试图使用IE v1或> v19访问你的页面将不会得到错误，所以可能更安全的做检查的Regex表达式如下代码:

var userAgent = navigator.userAgent.toLowerCase();
// Test if the browser is IE and check the version number is lower than 9
if (/msie/.test(userAgent) && 
    parseFloat((userAgent.match(/.*(?:rv|ie)[\/: ](.+?)([ \);]|$)/) || [])[1]) < 9) {
  // Navigate to error page
}

var isIE9OrBelow = function()
{
   return /MSIE\s/.test(navigator.userAgent) && parseFloat(navigator.appVersion.split("MSIE")[1]) < 10;
}

简单的解决方案，停止思考浏览器和使用年。

var year = eval(today.getYear());
if(year < 1900 )
 {alert('Good to go: All browsers and IE 9 & >');}
else
 {alert('Get with it and upgrade your IE to 9 or >');}

使用条件注释。您正在尝试检测IE < 9的用户，条件注释将在这些浏览器中工作;在其他浏览器(IE >= 10和非IE)中，注释将被视为正常的HTML注释，这就是它们的本质。

示例HTML:

<!--[if lt IE 9]>
WE DON'T LIKE YOUR BROWSER
<![endif]-->

如果你需要，你也可以用脚本来完成:

var div = document.createElement("div");
div.innerHTML = "<!--[if lt IE 9]><i></i><![endif]-->";
var isIeLessThan9 = (div.getElementsByTagName("i").length == 1);
if (isIeLessThan9) {
    alert("WE DON'T LIKE YOUR BROWSER");
}