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CSS media queries in JavaScript

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CSS media queries in JavaScript

· Web Dev Zone ·
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Deploying code to production can be filled with uncertainty. Reduce the risks, and deploy earlier and more often. Download this free guide to learn more. Brought to you in partnership with Rollbar.

I like the media queries feature added to CSS 3, that allows web application developers or designers to define styling sheets for a range of output devices. A media query consists of a media type and one or more expressions that limits the style sheet scope. I was wondering if JavaScript can be used to update the elements in page, say changing the source attribute of an image based on the device width. Turns out there is a function matchMedia which accepts a media query string as input and returns the result.


Here's how it works:

if (window.matchMedia('only screen and (max-width: 480px)').matches) //do something

The matchMedia function accepts a media query string and returns an object of type MediaQueryList. The matches property returns a boolean value true if the document matches the media query list. I wrote a very simple page that changes the image source when the window is resized, here's the code:

<!DOCTYPE HTML> 
<html> 
<head> 
<script> 
function onresize(event){ 
var deviceImage = document.getElementById('device-image'); 
//device is a phone 
if (window.matchMedia('only screen and (max-width: 480px)').matches) { 
deviceImage.src = "phone.png"; 
} 
//device is a tablet 
else if (window.matchMedia('only screen and (min-width: 481px) and (max-width: 1024px)').matches) { 
deviceImage.src = "tablet.png"; 
} 
//device is a notebook 
else { 
deviceImage.src = "notebook.png"; 
} 
} 

//change the image when window is resized 
window.addEventListener('resize', onresize, false); 

//show the image based on the device width 
window.addEventListener('load',onresize,false); 

</script> 
</head> 
<body> 
Resize the window 
<div align="center"> 
<img id="device-image" src="notebook.png" /> 
</div> 
</body> 
</html>

Here I'm checking for the min-width and max-width properties and then based on these values I'm changing the source attribute of the image. Here's the working demo:

 

Deploying code to production can be filled with uncertainty. Reduce the risks, and deploy earlier and more often. Download this free guide to learn more. Brought to you in partnership with Rollbar.

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