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Sniffing Out Mobile Devices with JavaScript

Hey, fellow devs! If you’ve been around the block a few times, you know the drill: your slick web app needs to play nice with mobile devices. But how do you tell a pocket-sized phone from a beefy desktop? That’s where JavaScript comes into play. Let’s dive into the nitty-gritty of detecting mobile devices with our favorite scripting language.

The Classic User-Agent Approach

Back in the good ol’ days, we’d sniff out the navigator.userAgent string like bloodhounds. It’s a quick and dirty way to get a sense of what device is hitting up your site.

function isMobile() {
  const ua = navigator.userAgent;
  return /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(ua);

if (isMobile()) {
  console.log("Rock on, mobile user!");

This regex checks for common mobile device keywords in the user-agent string. Simple, but not foolproof. Browsers evolve, and user-agent strings can be spoofed. Keep that in mind before you bet the farm on this method.

Modernizr to the Rescue

Ah, Modernizr, the Swiss Army knife of feature detection. If you’re not already using this gem, it’s time to give it a whirl. It’s great for detecting features, but we can also use it to detect touch events, which are a good proxy for mobile devices.

if (Modernizr.touchevents) {
  console.log("Touchy feely - must be mobile!");
} else {
  console.log("No touch for you - probably not mobile.");

Modernizr runs tests on browser features and adds classes to the HTML tag which you can use for CSS hooks or in your JavaScript logic. Neat, right?

MatchMedia to the Forefront

CSS media queries are the bread and butter of responsive design, but did you know you can use them in JavaScript too? window.matchMedia is your friend here.

function isMobileViewport() {
  return window.matchMedia("only screen and (max-width: 768px)").matches;

if (isMobileViewport()) {
  console.log("Viewport screams mobile!");

This function checks if the viewport width is 768 pixels or less, a common breakpoint for mobile devices. Remember, though, tablets in portrait mode might also fall into this range.

The Power of Libraries

Sometimes, you just want to stand on the shoulders of giants. Libraries like WURFL.js or mobile-detect.js can save you the headache of maintaining your own device detection logic.


WURFL.js taps into a massive database of device capabilities, so you’re not just detecting mobile; you’re getting a wealth of information.

WURFL.complete(function(info) {
  if (info.is_mobile) {
    console.log(`Device name: ${info.complete_device_name}`);


For a more lightweight approach, mobile-detect.js gives you straightforward device detection with a friendly API.

var MobileDetect = require('mobile-detect'),
    md = new MobileDetect(window.navigator.userAgent);

console.log(;  // 'Sony'
console.log(;   // 'Sony'
console.log(md.tablet());  // null

This library offers methods to differentiate between phones and tablets, which can be super handy.

And there you have it, the first half of our mobile detection saga. We’ve covered the basics, some old-school tactics, and a couple of trusty libraries. Stay tuned for the second half where we’ll dive into more advanced techniques and edge cases. Keep coding and stay mobile-friendly, folks!

Welcome back, code wranglers! We’ve already covered some ground on detecting mobile devices with JavaScript, but there’s more to explore. Let’s level up our game and tackle some advanced techniques to ensure our apps are as responsive as a caffeinated squirrel.

Orientation & Aspect Ratio Checks

Sometimes, the orientation and aspect ratio of the device can give us additional clues. Tablets, for example, might have the same resolution as some laptops, but their aspect ratio often differs.

function isLikelyMobileDevice() {
  const aspectRatio = window.innerWidth / window.innerHeight;
  return aspectRatio > 1 ? "Landscape" : "Portrait";

if (isLikelyMobileDevice() === "Portrait") {
  console.log("Portrait mode - higher chance of being a mobile device.");

Keep in mind that users can rotate their devices, so it’s wise to listen for orientation changes:

window.addEventListener("orientationchange", function() {
  console.log(`New orientation is: ${isLikelyMobileDevice()}`);

Feature Detection with CSS4 Media Queries

CSS4 brings some powerful media queries that JavaScript can leverage through matchMedia. One such feature is the pointer query, which can indicate how accurate the primary pointing device is.

function hasCoarsePointer() {
  return window.matchMedia("(pointer: coarse)").matches;

if (hasCoarsePointer()) {
  console.log("Coarse pointer detected - hello, touch screen!");

Devices with touch screens typically have a “coarse” pointer, whereas those with a mouse have a “fine” pointer.

Combining Techniques for Robust Detection

No single method is foolproof, but when you combine them, you get a much clearer picture. Here’s a composite function that takes into account user-agent, viewport, and feature detection:

function isDefinitelyMobile() {
  const uaIsMobile = isMobile(); // Our user-agent function from earlier
  const viewportIsMobile = isMobileViewport(); // Our viewport function from earlier
  const hasTouchEvents = 'ontouchstart' in window || navigator.maxTouchPoints > 0;

  return uaIsMobile || (viewportIsMobile && hasTouchEvents);

if (isDefinitelyMobile()) {
  console.log("All signs point to mobile!");

This function gives us a more confident assertion that we’re dealing with a mobile device.

Handling False Positives and Negatives

It’s important to remember that device detection is not an exact science. There will always be edge cases, like hybrid laptops with touch screens or gaming consoles with web browsers. Be prepared to handle these anomalies gracefully.

One way to mitigate false positives/negatives is to use feature detection to enable or disable specific functionality rather than to dictate the entire user experience. This way, even if a device is misidentified, the user can still access the core features of your application.

Performance Considerations

While it’s tempting to throw every detection method at your app, remember that each check takes time and can affect the user experience. Optimize by:

  • Caching results where possible.
  • Avoiding complex checks on critical rendering paths.
  • Using server-side detection to offload processing from the client.


Device detection is as much art as it is science. By combining various JavaScript techniques, you can get a pretty good idea of whether you’re dealing with a mobile device or not. Just remember to use these powers for good—enhance the user experience, don’t gatekeep it.

And that’s a wrap on our mobile detection deep dive. Whether you’re a seasoned vet or a fresh-faced newbie, I hope these insights help you build more responsive, user-friendly web apps. Keep pushing the boundaries, and always be ready to adapt because in the world of tech, change is the only constant. Happy coding!