Answers for "how to convert a php value to a javascript value"

js var to php

<script>
   var res = "success";
</script>
<?php
   echo "<script>document.writeln(res);</script>";
?>

how to change javascript value to php value

<script> 
  document.cookie = "js_var = " + This is used to chang js to php 
</script>
<?php
    $php_var= $_COOKIE['js_var'];
	echo $php_var;
?>