PHP Post not passing Variable when using JS

Hi guys

As part of my form, a user is allowed to pick a "closing date" using a JS calender

Here is the JS Script:

<script type="text/javascript" src="js/jsDatePick.min.1.3.js"></script>
<script type="text/javascript">
window.onload = function(){
new JsDatePick({
useMode:2,
target:"closingdate",
dateFormat:"%d-%m-%Y"
});
};
</script>


and the form input:

<input type="text" name="closingdate" style="width: 260px" value ="'.$closingdate.'" id="closingdate"></input>


When I select my date, and post the date, the variable is not carried accross

If I remove the id="closindate", and manually enter something into the text box, it works fine, that way I know its the JS that is causing the variable not to POST

Any help at all would be greatly appreciated

Many thanks in advance