Populating the birthday through a javascript loop

JavaScript
1

we’re just starting our lesson on JavaScript and i need to make a form that ask the user’s birthday on a drop down menu, but the day drop down menu ranges from 1-31 must be populated using a javascript loop and also the year. Then after the user selects the birthday, the age will be shown automatically.
I don’t know how to start :sick: please help

thank you in advance

2

just a little help from me:

<html>
    <head>
        <script language="javascript">
            function dgi(el)
            {
                return document.getElementById(el);
            }
            var aYear = 100;
            window.onload = function()
            {
                var y = dgi('year');
                var d = new Date();
                var _y = d.getFullYear();

                var _o = document.createElement('option');
                _o.setAttribute('value', 0);
                _o.innerHTML = 'Year';
                y.appendChild(_o);

                for(var i = 0; i < aYear; i++)
                {
                    var o = document.createElement('option');
                    o.setAttribute('value', _y);
                    o.innerHTML = _y;
                    y.appendChild(o);
                    _y--;
                }
            }
            function loadMonths(obj)
            {
                if(obj.value != '0')
                {
                    dgi('months').style.display = '';
                }
                else
                {
                    dgi('months').style.display = 'none';
                }
            }
            function loadDays(obj)
            {
                var days = dgi('days');
                    
                if(obj.value != '0')
                {
                    clearDays();
                    var number = 32 - new Date(parseInt(dgi('year').value), parseInt(dgi('months').value)-1, 32).getDate();
                    
                    for(var i = 1; i <= number; i++)
                    {
                        var o = document.createElement('option');
                        o.setAttribute('value', i);
                        o.innerHTML = i;
                        days.appendChild(o);
                    }
                    days.style.display = '';
                }
                else
                {
                    clearDays();
                    hideDays();
                }
            }
            function clearDays()
            {
                var days = dgi('days');
                days.innerHTML = '';                
            }

            function hideDays()
            {
                var days = dgi('days');
                days.style.display = 'none';
            }

        </script>
    </head>
    <body>
        <select id="year" onchange="loadMonths(this);">

        </select>
        <select id="months" style="display: none;" onchange="loadDays(this);">
            <option value="0">Month</option>
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
            <option value="5">5</option>
            <option value="6">6</option>
            <option value="7">7</option>
            <option value="8">8</option>
            <option value="9">9</option>
            <option value="10">10</option>
            <option value="11">11</option>
            <option value="12">12</option>
        </select>
        <select id="days" style="display: none;"></select>
    </body>
</html>