Answers for "how to add javascript value to php variable"

how to use javascript variable in php

<script>
var p1 = "success";
</script>

<?php
echo "<script>document.writeln(p1);</script>";
?>

how to use php variable in javascript file

<?php
    $color = "Red";
?>
<script type="text/javascript">var color = "<?= $color ?>";</script>
<script type="text/javascript" src="file.js"></script>