passing variables between javascript and JSP

i have a variable in jsp named "var" and i would like to assign to it a value from a java script .

How could i do this?

here is the code

<%

String var="firstletter"+ %><script>ar['0']</script><% +"the last letter";

%>

where ar['0'] is a java script array read from a java script file included as

<script src='ar1.js'>

</script>

in the header of the JSP

thanks in advance

[496 byte] By [iman_m_f] at [2007-9-18]