Before I go on, I want to mention the "noscript" tag. Because javascript is run on the client-side, and can be turned off (disabled), we want to consider the need for having something to cover a situation where the script cannot or does not run. The noscript tag

<noscript>
    <!-- non-javascript stuff goes here //-->
</noscript>

When would you use this? Whenever you have a script that SHOULD parse content necessary to a webpage, you'll want to have one of these to back it up. You don't need to use this if the script provides extra functionality that the page is not dependant on.

So how do we use a javascript?