JSFiddle - React, Tailwind, and code Playground

HTML

<div class="inline-inputs">
    <input type="text" id="dd" name="dd" placeholder="DD" maxlength="2" value="30">
    <input type="text" id="mm" name="mm" placeholder="MM" maxlength="2" value="02">
    <input type="text" id="yyyy" name="yyyy" placeholder="YYYY" value="2000" maxlength="4">
    <br>
    <input type="button" id="test" name="test" value="test">
</div>
<div id="result"></div>

JavaScript

$('#test').click(function(event) {

    var daySelector = "#dd",
        monthSelector = "#mm",
        yearSelector = "#yyyy";
    var day = $(daySelector).val() == "" ? 1 : parseInt($(daySelector).val(), 10);

    var month = $(monthSelector).val() == "" ? 1 : parseInt($(monthSelector).val(), 10);
    var year = parseInt($(yearSelector).val(), 10);
    var date = new Date(year, month, day);
    var result = (date.getFullYear() == year) && (date.getMonth() == month) && (date.getDate() == day);
    $('#result').append("<br>====================");
    $('#result').append("<br>day: " + day);    
    $('#result').append("<br>month: " + month);    
    $('#result').append("<br>year: " + year);    
    $('#result').append("<br>date.getTime(): " + date.getTime());    
    $('#result').append("<br>result: " + result);
    
});