JSFiddle - React, Tailwind, and code Playground

HTML

<p>Alis tarihi:
    <input type="text" id="tarih-alis" />
</p>
<p>Iade tarihi:
    <input type="text" id="tarih-iade" />
</p>
<p>Toplam gun:
    <input type="text" id="gun" />
</p>

JavaScript

$("#tarih-alis").datepicker({
    minDate: 0,maxDate: '+1Y+6M',onSelect: function (dateStr) {
        var min = $(this).datepicker('getDate');
        $("#Tarih-iade").datepicker('option', 'minDate', min || '0');
    }
});

$("#tarih-iade").datepicker({
    minDate: '0',maxDate: '+1Y+6M',onSelect: function (dateStr) {
        var max = $(this).datepicker('getDate');
        $('#datepicker').datepicker('option', 'maxDate', max || '+1Y+6M');
        var start = $("#tarih-alis").datepicker("getDate");
        var end = $("#tarih-iade").datepicker("getDate");
        var days = (end - start) / (1000 * 60 * 60 * 24);
        $("#gun").val(days);
    }
});