GZIP an javavascript
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I have a 80 kB javascript file, and I made some tests and concluded that after gzipping the size will be reduced to 34 kB.

I have googled 100 times and asked many people and they give me links like this

http://www.cyberciti.biz/tips/speed-up-apache-20-web-access-or-downloads-with-mod_deflate.html
http://httpd.apache.org/docs/2.0/mod/mod_deflate.html

I have read these a lot of times, but I can't gzip the js file

Please somebody explain me from where to start and where to go.
I thought I'll need to change something in .htaccess file, but no result. 

Thanks in advance