Difference between dates on onchange?

Question

JavaScript

The task is, when specifying two dates, to calculate the difference between them and send it via Ajax to PHP.

Two inputs with drop-down calendars:

Дата заезда<br/>
&lt;input id=&quot;date1&quot; class=&quot;date-pick&quot; name=&quot;address&quot; type=&quot;text&quot; value=&quot;&quot;&gt;<br/>
Дата выезда<br/>
&lt;input id=&quot;date2&quot; class=&quot;date-pick&quot; name=&quot;date2&quot; type=&quot;text&quot; onchange=&quot;update_cost('{$prod_id}',my_new&quot;&gt;<br/>

Script:

&lt;script language=&quot;javascript&quot;&gt;<br/>
var my_new;<br/>
my_new = my_day();<br/>
function my_day() {<br/>
var date1 = document.getElementById('date1').value;<br/>
var d1 = new Date(date1.replace(/(\d+).(\d+).(\d+)/, '$3/$2/$1'));<br/>
<br/>
var date2 = document.getElementById('date2').value;<br/>
var d2 = new Date(date2.replace(/(\d+).(\d+).(\d+)/, '$3/$2/$1'));<br/>
var d = d2.getTime() - d1.getTime();<br/>
return d/(1000*60*60*24);<br/>
}<br/>
&lt;/script&gt;<br/>

But for some reason it does not work, even with onchange="alert(my_new)" NaN is issued, although if you initially set value for inputs with dates, then everything works.

Answer 1

Surely drop-down calendars have their own method for getting the selected date value.