Gzip versus minify

Question

I had a somewhat lively discussion the other day about minifying Javascript and CSS versus someone who prefers using Gzip.

I'll call this person X.

X said that Gzip allready minifies the code, since it zips your files.

I disagree. Zip is a lossless method of shrinking filesize. Lossless means the original must be restored perfectly, meaning info must be stored to be able to restore the spaces, the un-needed characters, commented code and everything else. That takes up more space, since more must be compressed.

I have no method of testing, but I believe that the Gzip of this code:

.a1 {
    background-color:#FFFFFF;
    padding: 40px 40px 40px 40px;
}

Will still be bigger than the Gzip of this code:

.a1{body:background-color:#FFF;padding:40px}

Is there anybody who can prove this right or wrong.
And please don't come saying "It's right because that's what I've always used".

I am asking for scientific proof here.

Answer 1

You are correct, minify+gzip results in less bytes. No scientific proof though.

How come you have no method of testing?

Minify your code in one file, and leave it "unminified" on another. Upload to a webserver capable of gziping the output (mod_deflate for Apache, for example), install Firebug extension for firefox, clear your cache and access both files. Firebug's "NET" tab will contain the exact amount of data transfered, compare those and you have "empirical" proof.