How to force the browser to reload CSS and JavaScript files

When editing the CSS and JavaScript of a site, there is a slight chance that the user may get the old versions, which at best will cause a lot of complains and at worst will cost you a lot of lost customers. The reason for this is that browsers cache static content like CSS and JavaScript. However, telling a browser to reload them is not that hard to do. All it takes is a little trick that will force our friendly browsers into thinking that the CSS and JavaScript are dynamic content.

Before we go on, let us take a look at how we specify the CSS and JavaScript to be used within HTML. Normally we have something in the line of:

<link rel="StyleSheet" type="text/css" href="/static/style.css">

<script src="/static/js/script.js" type="text/javascript"></script>

Where style.css and script.js are our files. Naturally CSS files are specified with the href attribute of thelink tag, while JavaScript files are included using the script tag. Now, let’s take a look how we can make our browser reload CSS and JavaScript every time:

<link rel="StyleSheet" type="text/css" href="/static/style.css?version=15">

<script src="/static/js/script.js?version=15" type="text/javascript"></script>

“Now what is that “version”?”, you are probably thinking. Well it’s nothing. No really, it does absolutely nothing. You can use ?favouritesite=onlinehowto.net15 if you want. It would have the absolutely same effect.

“But what does it do?”, you are probably thinking. “This looks just like passing GET variables.” Exactly!

The browser cache uses a pretty complicated mechanism, but there is one thing that you should know for sure index.html?version=14 and index.html?version=15 are two different pages for the browsers, therefore it can’t rely on its cache, therefore it must get them again.

But what happens on the server side? Well those arguments are ignored by our server and it simply supplies style.css and script.js.

Whatever language, technology, etc. you are using, you always keep a header file which is included pretty much everywhere so changing the version=<number> part after each revision is pretty easy. You can even make it a part of your site’s logic.

In conclusion, this trick may save you a lot of headaches related to cached CSS and JavaScript, and if you believe you may have some issues, we greatly encourage you to use it!

SOURCE	LINK	LANGUAGE	ENGLISH