Hi,

<% String attachmentid="12345678" String encodedvalue=pega_rules_default.Base64Encode(attachmentid);%>

<script>

function testing(){

var jsvalue="<% =attachmentid %>";

var jsencodedvalue ="<%=encodedvalue%>";

}

</script>

converts the js variable value to base64 encoding. call the testing function and put a debugger in the code it will converts the js variable value to base64 encoding