Check if user is using IE

It's several years later, and the Edge browser now uses Chromium as its rendering engine.
Checking for IE 11 is still a thing, sadly.

Here is a more straightforward approach, as ancient versions of IE should be gone.

if (window.document.documentMode) {  // Do IE stuff}

Here is my old answer (2014):

In Edge the User Agent String has changed.

/** * detect IEEdge * returns version of IE/Edge or false, if browser is not a Microsoft browser */function detectIEEdge() {    var ua = window.navigator.userAgent;    var msie = ua.indexOf('MSIE ');    if (msie > 0) {        // IE 10 or older => return version number        return parseInt(ua.substring(msie + 5, ua.indexOf('.', msie)), 10);    }    var trident = ua.indexOf('Trident/');    if (trident > 0) {        // IE 11 => return version number        var rv = ua.indexOf('rv:');        return parseInt(ua.substring(rv + 3, ua.indexOf('.', rv)), 10);    }    var edge = ua.indexOf('Edge/');    if (edge > 0) {       // Edge => return version number       return parseInt(ua.substring(edge + 5, ua.indexOf('.', edge)), 10);    }    // other browser    return false;}

Sample usage:

alert('IEEdge ' + detectIEEdge());

Default string of IE 10:

Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; Trident/6.0)

Default string of IE 11:

Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv:11.0) like Gecko 

Default string of Edge 12:

Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.71 Safari/537.36 Edge/12.0 

Default string of Edge 13 (thx @DrCord):

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2486.0 Safari/537.36 Edge/13.10586 

Default string of Edge 14:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2486.0 Safari/537.36 Edge/14.14300 

Default string of Edge 15:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36 Edge/15.15063 

Default string of Edge 16:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36 Edge/16.16299 

Default string of Edge 17:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.140 Safari/537.36 Edge/17.17134 

Default string of Edge 18 (Insider preview):

Mozilla/5.0 (Windows NT 10.0; Win64; x64; ServiceUI 14) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.140 Safari/537.36 Edge/18.17730 

Test at CodePen:

http://codepen.io/gapcode/pen/vEJNZN

Use below JavaScript method :

function msieversion() {    var ua = window.navigator.userAgent;    var msie = ua.indexOf("MSIE ");    if (msie > 0) // If Internet Explorer, return version number    {        alert(parseInt(ua.substring(msie + 5, ua.indexOf(".", msie))));    }    else  // If another browser, return 0    {        alert('otherbrowser');    }    return false;}

You may find the details on below Microsoft support site :

How to determine browser version from script

Update : (IE 11 support)

function msieversion() {    var ua = window.navigator.userAgent;    var msie = ua.indexOf("MSIE ");    if (msie > 0 || !!navigator.userAgent.match(/Trident.*rv\:11\./))  // If Internet Explorer, return version number    {        alert(parseInt(ua.substring(msie + 5, ua.indexOf(".", msie))));    }    else  // If another browser, return 0    {        alert('otherbrowser');    }    return false;}

If all you want to know is if the browser is IE or not, you can do this:

var isIE = false;var ua = window.navigator.userAgent;var old_ie = ua.indexOf('MSIE ');var new_ie = ua.indexOf('Trident/');if ((old_ie > -1) || (new_ie > -1)) {    isIE = true;}if ( isIE ) {    //IE specific code goes here}

Update 1: A better method

I recommend this now. It is still very readable and is far less code :)

var ua = window.navigator.userAgent;var isIE = /MSIE|Trident/.test(ua);if ( isIE ) {  //IE specific code goes here}

Thanks to JohnnyFun in the comments for the shortened answer :)

Update 2: Testing for IE in CSS

Firstly, if you can, you should use @supports statements instead of JS for checking if a browser supports a certain CSS feature.

.element {  /* styles for all browsers */}@supports (display: grid) {  .element {    /* styles for browsers that support display: grid */  }}

(Note that IE doesn't support @supports at all and will ignore any styles placed inside an @supports statement.)

If the issue can't be resolved with @supports then you can do this:

// JSvar ua = window.navigator.userAgent;var isIE = /MSIE|Trident/.test(ua);if ( isIE ) {  document.documentElement.classList.add('ie')}

/* CSS */.element {  /* styles that apply everywhere */}.ie .element {  /* styles that only apply in IE */}

(Note: classList is relatively new to JS and I think, out of the IE browsers, it only works in IE11. Possibly also IE10.)

If you are using SCSS (Sass) in your project, this can be simplified to:

/* SCSS (Sass) */.element {  /* styles that apply everywhere */  .ie & {    /* styles that only apply in IE */  }}

Update 3: Adding Microsoft Edge (not recommended)

If you also want to add Microsoft Edge into the list, you can do the following. However I do not recommend it as Edge is a much more competent browser than IE.

var ua = window.navigator.userAgent;var isIE = /MSIE|Trident|Edge\//.test(ua);if ( isIE ) {  //IE & Edge specific code goes here}