Answers for "assign a php variable a value from js"

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;?>

how to change php variable value in javascript

<?php
$php_var = "This is used to change php values to js";
?>
<script>
var js_var = '<?php echo $php_var ;?>';
document.write(js_var);
</script>