How to force the browser to reload cached CSS/JS files?

Question

I have noticed that some browsers (in particular, Firefox and Opera) are very zealous in using cached copies of .css and .js files, even be

Answer 1

Simply add this code, where you want to do hard reload (force browser to reload cached CSS/JS files ) Do this inside the .load so it does not refreshes like a loop

 $( window ).load(function() {
   location.reload(true);
});

Answer 2

Interesting post. Having read all the answers here combined with the fact that I have never had any problems with "bogus" query strings (which I am unsure why everyone is so reluctant to use this) I guess the solution (which removes the need for apache rewrite rules as in the accepted answer) is to compute a short HASH of the CSS file contents (instead of the file datetime) as a bogus querystring.

This would result in the following:

<link rel="stylesheet" href="/css/base.css?[hash-here]" type="text/css" />

Of course the datetime solutions also get the job done in the case of editing a CSS file but I think it is about the css file content and not about the file datetime, so why get these mixed up?

Answer 3

Just use server side code to add the date of the file... that way it WILL be cached and only reloaded when the file changes

In ASP.NET

<link rel="stylesheet" href="~/css/custom.css?d=@(System.Text.RegularExpressions.Regex.Replace(File.GetLastWriteTime(Server.MapPath("~/css/custom.css")).ToString(),"[^0-9]", ""))" />

<script type="text/javascript" src="~/js/custom.js?d=@(System.Text.RegularExpressions.Regex.Replace(File.GetLastWriteTime(Server.MapPath("~/js/custom.js")).ToString(),"[^0-9]", ""))"></script>    

This can be simplified to:

<script src="<%= Page.ResolveClientUrlUnique("~/js/custom.js") %>" type="text/javascript"></script>

By adding an extension method to your project to extend Page:

public static class Extension_Methods
{
    public static string ResolveClientUrlUnique(this System.Web.UI.Page oPg, string sRelPath)
    {
        string sFilePath = oPg.Server.MapPath(sRelPath);
        string sLastDate = System.IO.File.GetLastWriteTime(sFilePath).ToString();
        string sDateHashed = System.Text.RegularExpressions.Regex.Replace(sLastDate, "[^0-9]", "");

        return oPg.ResolveClientUrl(sRelPath) + "?d=" + sDateHashed;
    }
}

Answer 4

I've heard this called "auto versioning". The most common method is to include the static file's mtime somewhere in the URL, and strip it out using rewrite handlers or URL confs:

See also:

• Automatic asset versioning in Django
• Automatically Version Your CSS and JavaScript Files

Answer 5

Thanks at Kip for his perfect solution!

I extended it to use it as an Zend_view_Helper. Because my client run his page on a virtual host I also extended it for that.

Hope it helps someone else too.

/**
 * Extend filepath with timestamp to force browser to
 * automatically refresh them if they are updated
 *
 * This is based on Kip's version, but now
 * also works on virtual hosts
 * @link http://stackoverflow.com/questions/118884/what-is-an-elegant-way-to-force-browsers-to-reload-cached-css-js-files
 *
 * Usage:
 * - extend your .htaccess file with
 * # Route for My_View_Helper_AutoRefreshRewriter
 * # which extends files with there timestamp so if these
 * # are updated a automatic refresh should occur
 * # RewriteRule ^(.*)\.[^.][\d]+\.(css|js)$ $1.$2 [L]
 * - then use it in your view script like
 * $this->headLink()->appendStylesheet( $this->autoRefreshRewriter($this->cssPath . 'default.css'));
 *
 */
class My_View_Helper_AutoRefreshRewriter extends Zend_View_Helper_Abstract {

    public function autoRefreshRewriter($filePath) {

        if (strpos($filePath, '/') !== 0) {

            // path has no leading '/'
            return $filePath;
        } elseif (file_exists($_SERVER['DOCUMENT_ROOT'] . $filePath)) {

            // file exists under normal path
            // so build path based on this
            $mtime = filemtime($_SERVER['DOCUMENT_ROOT'] . $filePath);
            return preg_replace('{\\.([^./]+)$}', ".$mtime.\$1", $filePath);
        } else {

            // fetch directory of index.php file (file from all others are included)
            // and get only the directory
            $indexFilePath = dirname(current(get_included_files()));

            // check if file exist relativ to index file
            if (file_exists($indexFilePath . $filePath)) {

                // get timestamp based on this relativ path
                $mtime = filemtime($indexFilePath . $filePath);

                // write generated timestamp to path
                // but use old path not the relativ one
                return preg_replace('{\\.([^./]+)$}', ".$mtime.\$1", $filePath);
            } else {

                return $filePath;
            }
        }
    }

}

Cheers and thanks.

Answer 6

Have not found the client sided DOM approach creating the script node (or css) element dynamically:

<script>
    var node = document.createElement("script"); 
    node.type = "text/javascript";
    node.src = 'test.js?'+Math.floor(Math.random()*999999999);
    document.getElementsByTagName("head")[0].appendChild(node);
</script>