Correct way to use Modernizr to detect IE?

Modernizr doesn't detect browsers as such, it detects which feature and capability are present and this is the whole jist of what it's trying to do.

You could try hooking in a simple detection script like this and then using it to make your choice. I've included Version Detection as well just in case that's needed. If you only want to check of any version of IE you could just look for the navigator.userAgent having a value of "MSIE".

var BrowserDetect = {
        init: function () {
            this.browser = this.searchString(this.dataBrowser) || "Other";
            this.version = this.searchVersion(navigator.userAgent) || this.searchVersion(navigator.appVersion) || "Unknown";
        },
        searchString: function (data) {
            for (var i = 0; i < data.length; i++) {
                var dataString = data[i].string;
                this.versionSearchString = data[i].subString;

                if (dataString.indexOf(data[i].subString) !== -1) {
                    return data[i].identity;
                }
            }
        },
        searchVersion: function (dataString) {
            var index = dataString.indexOf(this.versionSearchString);
            if (index === -1) {
                return;
            }

            var rv = dataString.indexOf("rv:");
            if (this.versionSearchString === "Trident" && rv !== -1) {
                return parseFloat(dataString.substring(rv + 3));
            } else {
                return parseFloat(dataString.substring(index + this.versionSearchString.length + 1));
            }
        },

        dataBrowser: [
            {string: navigator.userAgent, subString: "Edge", identity: "MS Edge"},
            {string: navigator.userAgent, subString: "MSIE", identity: "Explorer"},
            {string: navigator.userAgent, subString: "Trident", identity: "Explorer"},
            {string: navigator.userAgent, subString: "Firefox", identity: "Firefox"},
            {string: navigator.userAgent, subString: "Opera", identity: "Opera"},  
            {string: navigator.userAgent, subString: "OPR", identity: "Opera"},  

            {string: navigator.userAgent, subString: "Chrome", identity: "Chrome"}, 
            {string: navigator.userAgent, subString: "Safari", identity: "Safari"}       
        ]
    };
    
    BrowserDetect.init();
    document.write("You are using <b>" + BrowserDetect.browser + "</b> with version <b>" + BrowserDetect.version + "</b>");

You can then simply check for:

BrowserDetect.browser == 'Explorer';
BrowserDetect.version <= 9;

You can use Modernizr to detect simply IE or not IE, by checking for SVG SMIL animation support.

If you've included SMIL feature detection in your Modernizr setup, you can use a simple CSS approach, and target the .no-smil class that Modernizr applies to the html element:

html.no-smil {
  /* IE/Edge specific styles go here - hide HTML5 content and show Flash content */
}

Alternatively, you could use Modernizr with a simple JavaScript approach, like so:

if ( Modernizr.smil ) {
  /* set HTML5 content */
} else {
  /* set IE/Edge/Flash content */
}

Bear in mind, IE/Edge might someday support SMIL, but there are currently no plans to do so.

For reference, here's a link to the SMIL compatibility chart at caniuse.com.


Detecting CSS 3D transforms

Modernizr can detect CSS 3D transforms, yeah. The truthiness of Modernizr.csstransforms3d will tell you if the browser supports them.

The above link lets you select which tests to include in a Modernizr build, and the option you're looking for is available there.


Detecting IE specifically

Alternatively, as user356990 answered, you can use conditional comments if you're searching for IE and IE alone. Rather than creating a global variable, you can use HTML5 Boilerplate's <html> conditional comments trick to assign a class:

<!--[if lt IE 7]>      <html class="no-js lt-ie9 lt-ie8 lt-ie7"> <![endif]-->
<!--[if IE 7]>         <html class="no-js lt-ie9 lt-ie8"> <![endif]-->
<!--[if IE 8]>         <html class="no-js lt-ie9"> <![endif]-->
<!--[if gt IE 8]><!--> <html class="no-js"> <!--<![endif]-->

If you already have jQuery initialised, you can just check with $('html').hasClass('lt-ie9'). If you need to check which IE version you're in so you can conditionally load either jQuery 1.x or 2.x, you can do something like this:

myChecks.ltIE9 = (function(){
    var htmlElemClasses = document.querySelector('html').className.split(' ');
    if (!htmlElemClasses){return false;}
    for (var i = 0; i < htmlElemClasses.length; i += 1 ){
      var klass = htmlElemClasses[i];
      if (klass === 'lt-ie9'){
        return true;
      }
    }
    return false;
}());

N.B. IE conditional comments are only supported up to IE9 inclusive. From IE10 onwards, Microsoft encourages using feature detection rather than browser detection.


Whichever method you choose, you'd then test with

if ( myChecks.ltIE9 || Modernizr.csstransforms3d ){
    // iframe or flash fallback
} 

Don't take that || literally, of course.


If you're looking for a JS version (using a combination of feature detection and UA sniffing) of what html5 boilerplate used to do:

var IE = (!! window.ActiveXObject && +(/msie\s(\d+)/i.exec(navigator.userAgent)[1])) || NaN;
if (IE < 9) {
    document.documentElement.className += ' lt-ie9' + ' ie' + IE;
}

Well, after doing more research on this topic I ended up using following solution for targeting IE 10+. As IE10&11 are the only browsers which support the -ms-high-contrast media query, that is a good option without any JS:

@media screen and (-ms-high-contrast: active), screen and (-ms-high-contrast: none) {  
   /* IE10+ specific styles go here */  
}

Works perfectly.