Invoking Java Script

There are two places where Java Script can be used in HTML, inline events and <script> tags:

// inline event
<div onclick="new Effect.Appear('mydiv')">click me</div>

// script tag
<script type="text/javascript">
// <![CDATA[
  new Effect.Appear('mydiv');
// ]]>
</script>

// script tag refering to an external JavaScript file
<script src="prototype.js" type="text/javascript"></script>

Events can also be created programmatically (e.g. with the Prototype library Event.observe function).

See Wikipedia for a more thorough description of JavaScript