Which MIME type to compress? and what If I omit the `type` attribute from the HTML?

Question

Per my request, my webhost had turned mod_deflate ON.

In my Cpanel I now have an "Optimize Website" button.

Inside that menu I could either choose:

"Compress all content" or "Compress the specified MIME types" with the following default MIME types: "text/html text/plain text/xml"

1. Which option should I choose and why?

2. If I choose option 2, which types should I add (is there a recommended list with the exact way they should be written)?

3. According to Google recommendations, I have omitted the type="text/css" attributes from all CSS references, as well as the type="text/javascript" attributes from all script references. Would this hinder the "gzipping" process?

Solution

Which option should I choose and why?

I would probably choose the second option, but add to that list text/css and text/javascript.

Basically you want to compress any text-based content, but not content like images, as these are already compressed.

I have omitted the type="text/css" attributes from all CSS references, as well as the type="text/javascript" attributes from all script references. Would this hinder the "gzipping" process?

That looks like Google's internal style guide, it's not meant for your website. However I wouldn't expect any issues from omitting mime types in that way. They're not required in HTML5.

Comments

[rockyraw]

Thanks, though In addition to the text/html text/plain text/xml and the text/javascript text/css you suggested, I've also added application/x-javascript application/javascript application/xhtml+xml, as without this, .js file would not be compressed (saw the size difference on my server log). I just wonder whether this is now enough, and what could be a possible drawback of simply choosing "compress all"?

[Tim Fountain]

Well, it depends a bit on whether 'compress all' means literally that. But like I said, you don't want to compress things like images, as they are already compressed. So you waste server resources by doing so.

[Arne Kröger]

@rockyraw The server does the gzipping but won't inspect your HTML attributes so, no, removing the 'type' attributes won't affect gzipping but, as stated, HTML5 doesn't require it and browsers have used the default for years.