How to detect a mobile device with JavaScript?

Testing for user agent is complex, messy and invariably fails. I also didn't find that the media match for "handheld" worked for me. The simplest solution was to detect if the mouse was available. And that can be done like this:

let isMouseAvailable = window.matchMedia("(any-pointer:coarse)").matches;

That will tell you if you need to show hover items or not and anything else that requires a physical pointer. The sizing can then be done on further media queries based on width.

The following little library is a belt braces version of the query above, should cover most "are you a tablet or a phone with no mouse" scenarios.

https://patrickhlauke.github.io/touch/touchscreen-detection/

Media matches have been supported since 2015 and you can check the compatibility here: https://caniuse.com/#search=matchMedia

In short you should maintain variables relating to whether the screen is touch screen and also what size the screen is. In theory I could have a tiny screen on a mouse operated desktop.

The cleanest way of finding device type is:

if (navigator.userAgentData.mobile) { // do something }

(although it isn't yet supported on Safari)

More info: https://developer.mozilla.org/en-US/docs/Web/API/NavigatorUAData/mobile

Another possibility is to use mobile-detect.js. Try the demo.

Browser usage:

<script src="mobile-detect.js"></script>
<script>
    var md = new MobileDetect(window.navigator.userAgent);
    // ... see below
</script>

Node.js / Express:

var MobileDetect = require('mobile-detect'),
    md = new MobileDetect(req.headers['user-agent']);
// ... see below

Example:

var md = new MobileDetect(
    'Mozilla/5.0 (Linux; U; Android 4.0.3; en-in; SonyEricssonMT11i' +
    ' Build/4.1.A.0.562) AppleWebKit/534.30 (KHTML, like Gecko)' +
    ' Version/4.0 Mobile Safari/534.30');

// more typically we would instantiate with 'window.navigator.userAgent'
// as user-agent; this string literal is only for better understanding

console.log( md.mobile() );          // 'Sony'
console.log( md.phone() );           // 'Sony'
console.log( md.tablet() );          // null
console.log( md.userAgent() );       // 'Safari'
console.log( md.os() );              // 'AndroidOS'
console.log( md.is('iPhone') );      // false
console.log( md.is('bot') );         // false
console.log( md.version('Webkit') );         // 534.3
console.log( md.versionStr('Build') );       // '4.1.A.0.562'
console.log( md.match('playstation|xbox') ); // false

As I (kind of without success) searched for the proper solution for my hack, I want to add my hack here nonetheless: I simply check for support of device orientation, which seems the most significant diffrence between mobiles and desktop:

var is_handheld=0; // just a global if(window.DeviceOrientationEvent) {is_handheld=1;}

That being said, imho a page should also offer manual choice between mobile / desktop layout. I got 1920*1080 and I can zoom in - an oversimplified and feature-reduced wordpressoid chunk is not always a good thing. Especially forcing a layout based on nonworking device detection - it happens all the time.

Similar to several of the answers above. This simple function, works very well for me. It is current as of 2019

function IsMobileCard()
{
var check =  false;

(function(a){if(/(android|bb\d+|meego).+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|mobile.+firefox|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)\/|plucker|pocket|psp|series(4|6)0|symbian|treo|up\.(browser|link)|vodafone|wap|windows ce|xda|xiino/i.test(a)||/1207|6310|6590|3gso|4thp|50[1-6]i|770s|802s|a wa|abac|ac(er|oo|s\-)|ai(ko|rn)|al(av|ca|co)|amoi|an(ex|ny|yw)|aptu|ar(ch|go)|as(te|us)|attw|au(di|\-m|r |s )|avan|be(ck|ll|nq)|bi(lb|rd)|bl(ac|az)|br(e|v)w|bumb|bw\-(n|u)|c55\/|capi|ccwa|cdm\-|cell|chtm|cldc|cmd\-|co(mp|nd)|craw|da(it|ll|ng)|dbte|dc\-s|devi|dica|dmob|do(c|p)o|ds(12|\-d)|el(49|ai)|em(l2|ul)|er(ic|k0)|esl8|ez([4-7]0|os|wa|ze)|fetc|fly(\-|_)|g1 u|g560|gene|gf\-5|g\-mo|go(\.w|od)|gr(ad|un)|haie|hcit|hd\-(m|p|t)|hei\-|hi(pt|ta)|hp( i|ip)|hs\-c|ht(c(\-| |_|a|g|p|s|t)|tp)|hu(aw|tc)|i\-(20|go|ma)|i230|iac( |\-|\/)|ibro|idea|ig01|ikom|im1k|inno|ipaq|iris|ja(t|v)a|jbro|jemu|jigs|kddi|keji|kgt( |\/)|klon|kpt |kwc\-|kyo(c|k)|le(no|xi)|lg( g|\/(k|l|u)|50|54|\-[a-w])|libw|lynx|m1\-w|m3ga|m50\/|ma(te|ui|xo)|mc(01|21|ca)|m\-cr|me(rc|ri)|mi(o8|oa|ts)|mmef|mo(01|02|bi|de|do|t(\-| |o|v)|zz)|mt(50|p1|v )|mwbp|mywa|n10[0-2]|n20[2-3]|n30(0|2)|n50(0|2|5)|n7(0(0|1)|10)|ne((c|m)\-|on|tf|wf|wg|wt)|nok(6|i)|nzph|o2im|op(ti|wv)|oran|owg1|p800|pan(a|d|t)|pdxg|pg(13|\-([1-8]|c))|phil|pire|pl(ay|uc)|pn\-2|po(ck|rt|se)|prox|psio|pt\-g|qa\-a|qc(07|12|21|32|60|\-[2-7]|i\-)|qtek|r380|r600|raks|rim9|ro(ve|zo)|s55\/|sa(ge|ma|mm|ms|ny|va)|sc(01|h\-|oo|p\-)|sdk\/|se(c(\-|0|1)|47|mc|nd|ri)|sgh\-|shar|sie(\-|m)|sk\-0|sl(45|id)|sm(al|ar|b3|it|t5)|so(ft|ny)|sp(01|h\-|v\-|v )|sy(01|mb)|t2(18|50)|t6(00|10|18)|ta(gt|lk)|tcl\-|tdg\-|tel(i|m)|tim\-|t\-mo|to(pl|sh)|ts(70|m\-|m3|m5)|tx\-9|up(\.b|g1|si)|utst|v400|v750|veri|vi(rg|te)|vk(40|5[0-3]|\-v)|vm40|voda|vulc|vx(52|53|60|61|70|80|81|83|85|98)|w3c(\-| )|webc|whit|wi(g |nc|nw)|wmlb|wonu|x700|yas\-|your|zeto|zte\-/i.test(a.substr(0,4))) check = true;})(navigator.userAgent||navigator.vendor||window.opera);

return check;   
}