Help Spoofing User-Agent / Browser-Agent

[zaenal5757`]

Hello guys,
First of all I am very sorry because I am not that good in website coding, you can call me noob I know because that is the truth :(.

I would like to spoof the user-agent/browsing agent of the visitors coming on my website by using a script or javascript code if possible. Because I use .html not .php as my extensions.

I already use the search button but no luck. Tried google also but cannot understand.
Found this but I'm not sure how to use or where to put these codes.

window.navigator.__defineGetter__('userAgent', function () {
return 'Mozilla/5.0 (iPad; CPU OS 5_1_1 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Mobile/9B206';
});

Though I am not sure if that code is correct. Please anybody can help me?

Thank you so much and have a nice weekends.