why use this varibale?
 

hello guys,
i see in headinclude template

<script type="text/javascript">
<!--
var SESSIONURL = "$session[sessionurl_js]";
var SECURITYTOKEN = "$bbuserinfo[securitytoken]";
var IMGDIR_MISC = "$stylevar[imgdir_misc]";
var vb_disable_ajax = parseInt("$vboptions[disable_ajax]", 10);
// -->
</script>

why use this codes? if we not use, what will do?

If you don't use them it will likely break built in vBulletin JavaScripts. Those lines define CONSTANTS that are used in forum javascript scripts.