年月日时间选择

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>时间选择</title>
<script type="text/javascript">
    function doyear(){
        var select = document.getElementById("year");
        var thisYear = new Date().getFullYear();
        for(var i=1900;i<=thisYear;i++){
            var option = document.createElement("option");
            option.value = i;
            option.innerText = i;
            select.appendChild(option);
        }
    }

    function domoth(){
        var select = document.getElementById("month");
        for(var i=1;i<=12;i++){
            var option = document.createElement("option");
            option.value = i;
            option.innerText = i;
            select.appendChild(option);
        }
    }

    function doday(){
        var select = document.getElementById("day");
        var selectYear = parseInt(year.options[year.selectedIndex].value);
        var selectMonth = parseInt(month.options[month.selectedIndex].value);
        var date = new Date(selectYear,selectMonth,0);

        for(var i=1;i<=date.getDate();i++){
            var option = document.createElement("option");
            option.value = i;
            option.innerText = i;
            select.appendChild(option);
        }
    }

    function deleteOldChildNodes(){
        var day = document.getElementById("day");
        var node=day.firstChild;
        var tmpNode;
        while(node!=day.lastChild){
            tmpNode = node.nextSibling;
            day.removeChild(node);
            node = tmpNode;
        }
        day.removeChild(day.lastChild);
    }

    function pageInit(){
        doyear();
        domoth();
        doday();
        year.onchange = function(){deleteOldChildNodes();doday();};
        month.onchange = function(){deleteOldChildNodes();doday();};
    }
</script>
</head>
    <body>
        <div onclick="pageInit()"/>
            <select name="year" id="year"></select>年
            <select name="month" id="month"></select>月
            <select name="day" id="day"></select>日
    </body>
</html>