Answers for "how to echo javascript var to php variable"

using js variable in php

<script type="text/javascript">
var abc= 'this is text';
<?php $abc = "<script>document.write(abc)</script>"?>   
</script>
<?php echo $abc;?>

php variable as javascript function parameter in echo

<?php echo "<script> autoFill(".$dropDown.", ".$emptyDropDown."); </script>"; ?>