php与js互相调用

php中调用js

<?php 
echo '<script>var yearid=$("#yearId").val()</script>';
echo $yearid='<script>document.write(yearid);</script>';
?>

js中调用php

<?php
$userId=100;
?>
 <script>
var userId;
userId=$("#userId").value;
alert (userId);
</script>
<input type="text" name="userId" id="userId" value="<?php echo $userId; ?>">