//
the double slash comments out anything after it, just on that one line
/* */
anything between the slash-star and star-slash is considered a comment. the star-slash can be on a subsequent line if desired.
Code:
<script type="text/javascript"> //<![CDATA[ a = 2; // comment goes here // this is another comment /* and this is yet another comment */ b = 3; document.write("a=", a, ", b=", b); //]]> </script>
Output: