Using Session variables in Javascript

One of the common problems Web Developers face is interaction between client side and server side scripts. With the advent of AJAX it has become very simple.
But there are situations were we need to change the JavaScript variables dynamically without changing the rest of the script. For example some flash elements require JavaScript variables for their functionality like keeping track of the tabs.
This can be achieved very easily through the use of session variable as follows:

<script type="text/javascript" language="javascript">

function myFunction()
{
var var1=21;
var var2=<%=Convert.ToString(Session["myVariable"])%>
------
------
------

}

</script>

All you need to do is assign the session variable with the value you want on the page load in code behind.

I was quiet curious and also tried the vice verse i.e assigning a Session Variable in JavaScript. But it doesn't work !!!! Have to use alternate methods. If any one knows a way of doing so..Please Comment