Languages such as PHP/ASP/Python/Perl reside on the web server itself, and spit out all the dynamic content via HTML which is read & displayed by the browser. Modern websites usually have a SCRIPT element that links to an external javascript file which controls the behavior of the website. Javascript should be treated like icing on a cake, never rely on it (well an exception would be if you wanted to make a 100% js application such as Gmail/Google Maps) but on a regular website you should never rely upon JS being there, since it can easily be disabled (some (govt?) companies do this).