Question

I’ve seen a number of references to gzipping a javascript to save download time. But I also see a number of warnings that certain browsers do not support this.

I have two different methods at my disposal:

1. use mod_deflate to make Apache compress JS/CSS files in a given directory through htaccess
2. use ob_start('gzhandler') to compress a file and return it to the browser with the correct headers.

The problems with method 1 are that not all browsers support mod_deflate, and I have no clue how to write the .htaccess file to be smart enough to adjust for this.

The problem with method 2 is that there is no definitive answer about how to tell if a browser supports a gzipped script, or stylesheet, and that if it does what mime-type must be given as the content type in the header.

I need some advice. First, which method is more universally accepted by browsers? Second, how do I decay using either method to provide the uncompressed backup script? Third, would <script src='js/lib.js.gz' type='text/javascript'></script> work by itself? (It obviously wouldn’t decay.)

For the record, I’m using PHP5 with mod_deflate and full gzip creation capabilities, and my doctype is xhtml strict. Also, the javascript itself is compressed with YUI. Edit: I just went back and looked, but I have only Apache 1.3; I thought I had 2, so sorry for mentioning mod_deflate when I probably don’t have it.

Answer 1

mod_deflate and php’s gzhandler both are based on zlib, so in that sense there is little difference to a browser how the content is being compressed.

in response to your first concern, you can set module specific .htaccess info like this:

<IfModule mod_deflate.c>   # stuff </IfModule> 

in response to your second concern, you can detect for browser support in PHP:

if (strstr($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') ) {   ob_start('ob_gzhandler');   header('Content-Encoding: gzip'); // etc... } 

here’s some untested .htaccess that should be able to handle negotiation of compressed vs uncompressed .js files: (source)

<FilesMatch '\\.js.gz$'>   ForceType text/javascript   Header set Content-Encoding: gzip </FilesMatch> <FilesMatch '\\.js$'>   RewriteEngine On   RewriteCond %{HTTP_USER_AGENT} !'.*Safari.*'   RewriteCond %{HTTP:Accept-Encoding} gzip   RewriteCond %{REQUEST_FILENAME}.gz -f   RewriteRule (.*)\.js$ $1\.js.gz [L]   ForceType text/javascript </FilesMatch>