Javascript doesn't work

Hi. I am fairly new to WordPress. I use the online version of WordPress. I noticed that when i try to put in javascript into the text widgit, it deletes the javascript and it doesnt work. Im just copying and pasting this javascript from this site so I can put this really cool thing on my blog but it doesn’t work. Please help me. This has been going on for a while and i really dont know what to do.