Passing PHP variable to JQuery datepicker?

Question

I've explored many threads and my problem still isn't solved.

I have a JQuery datepicker:

<input id="datepicker" name="date" class="mydatepicker" onchange="isValidDate()"></input>

I'm trying to pass a PHP variable to this JQuery line:

$('#datepicker').datepicker('setDate', "<?php echo $UpdatedDataLogDate; ?>");

if it's length is greater than 5. So far I have this:

<?php

if(strlen($_SESSION['DataLogDate'])>5){

$DataLogDate = $_SESSION['DataLogDate'];
$UpdatedDataLogDate = date('m/d/Y', strtotime($DataLogDate));

echo "<script> hi(); </script>";
}

?>

<script type="text/javascript">
$(document).ready(hi() {
$('#datepicker').datepicker('setDate', "<?php echo $UpdatedDataLogDate; ?>");
});
</script>

<script type="text/javascript">
$(document).ready(function() {
        $("#datepicker").datepicker();

</script>

datepicker is tied to these files:

<link href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/base/jquery-ui.css" rel="stylesheet" type="text/css"/>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>
<script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/jquery-ui.min.js"></script>

Answer 1

<script type="text/javascript">
$(document).ready(function() {
$("#datepicker").datepicker();
$('#datepicker').datepicker('setDate', "<?php echo $UpdatedDataLogDate; ?>");
if($('#datepicker').datepicker("getDate")!== null){
$('#datepicker').css({"background-color": "#BFFFBF"});
}
check();  
});
</script>

<script type="text/javascript">
function check(){
if($('#datepicker').datepicker("getDate")!== null){
isValidDate();
}
}
</script>

isValidDate() is a javascript function that validates the date ... if validated, user can easily move on to next page (way our JavaScript is set up) ...