jQuery datepicker, add certain number of days once date selected - php

Question

Once the user has selected the date from the datepicker, i want to add 41 days.
<script language="javascript">
$(document).ready(function() {
$("#startdate").datepicker({ dateFormat: 'd/m/y'});
$('#startdate').datepicker({
onSelect: function(dateStr) {
var nights = parseInt($('#numofdays').val());
var depart = $.datepicker.parseDate('d/m/y', dateStr);
depart.setDate(depart.getDate('d/m/y') + nights);
$('#calc').val(depart);
}
});
});
</script>
Start: <input type="text" id="startdate" class="datepicker"><br />
<input type="hidden" id="numofdays" value="41"><br />
Calc: <input type="text" id="calc">

Answer 1

You might just need to combine the options in the same initiating function:
$("#startdate").datepicker({
dateFormat: 'd/m/y',
onSelect: function(dateStr, inst) {
var nights = parseInt($('#numofdays').val());
var depart = $.datepicker.parseDate('d/m/y', dateStr);
depart.setDate(depart.getDate('d/m/y') + nights);
$('#calc').val(depart.toLocaleDateString());
}
});
See this in action: http://jsfiddle.net/william/L9Szd/.

Answer 2

$('#startdate').datepicker('getDate') will return a Date object
d = $('#startdate').datepicker('getDate');
d.setDate(d.getDate()+nights); // add int nights to int date
alert(d);
Adding d.getDate() and nights will jump time forward. So if 9/16/2011 + 41 days you'll get 10/25/2011

Answer 3

would seem strange as a user to select a date, and then the box says a date that's 41 days later instead of the one I picked. why not do this addition server side with PHP?
$date_string = date('Y-m-d', strtotime('+41 days', strtotime($_POST['date_input'])));

Answer 4

This is the only simple way I found to do this:
To set date to 41 days ahead of the selected date:
1.Fetch selected date from a datepicker field
var newdate = new Date($("#datepicker_date_field_1").datepicker("getDate"));
2.Increase the date got from above
newdate.setDate(newdate.getDate() + 41);
3.Assign the newly formed date to another (or same) datepicker field
$("#datepicker_date_field_2").datepicker("setDate",newdate);