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Asked: 2026-06-09T20:58:46+00:00

I am trying to create a drop down calendar. No jquery! Pure javascript. So

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I am trying to create a drop down calendar. No jquery! Pure javascript. So far @rlemon has provided me great assistance and I have been able to build off code he has helped me with. I am almost finished, but am having a few small problems. So far everything works correctly, but now I am moving onto incorporating leap years which is where I am having problems. I am having trouble determining the current year that is selected. I have 

sel_year.onchange = recalculateDays2(this);

which I believe is passing the value of the current year selected. Then in the function recalculateDays2 I am creating a variable 

year_index = x.text;

which is supposed to be something like year_index = 2011, 2012 etc. I want the function recalculateDays2 to set feb days to 29 when the user has changed to the year 2012. Please help…

<html>
<head>
</head>
<body>
Calendar<br>
<hr align="left" width="200px"/>
--Year ------ Month ----- Day<br>
<div id="calendar-container"></div>
<script type="text/javascript">
(function() {
    var yr1 = 2011, yr2 = 2012, yr3 = 2013, yr4 = 2014;
    var years = [yr1, yr2, yr3, yr4];
    var calendar = [
        ["January", 31],["February", 28],["March", 31],["April", 30],["May", 31],["June", 30],["July", 31],["August", 31],["September", 30],["October", 31],["November", 30],["December", 31]],
        //this is the variable that accesses the content
        cont = document.getElementById('calendar-container');
    //creates the variables for the drop downs
    var sel_year = document.createElement('select'), sel_month = document.createElement('select'), sel_day = document.createElement('select');

    function createOption(txt, val) {
        //this creates the option but it seems that it is making the value -1 than what the text node is
        var option = document.createElement('option');
        option.value = val;
        option.appendChild(document.createTextNode(txt));
        return option;
    }

    function createYearOption(val) {
        var option = document.createElement('option');
        option.value = val;
        option.appendChild(document.createTextNode(val));
        return option;
    }

    //this clears any elements for days, months, years
    function clearChildren(ele) {
        while (ele.hasChildNodes()) {
            ele.removeChild(ele.lastChild);
        }
    }

    //this function is only triggered when you recalculate the months
    function recalculateDays() {
        var month_index = sel_month.value,
            df = document.createDocumentFragment();
        //l is the variable for the number of days in the month from the array above ex:28, 30, 31
        for (var i = 0, l = calendar[month_index][1]; i < l; i++) {
            //the first variable is what number will be displayed in the day drop down
            df.appendChild(createOption(i + 1, i));
        }
        clearChildren(sel_day);
        sel_day.appendChild(df);
    }

    //this function is triggered only when you change the year
    function recalculateDays2(x) {
        var month_index = sel_month.value,
            df = document.createDocumentFragment(), 
            year_index = x.text;
        //this checks to see if the month selected is Feb   
        if ((month_index == 1) && (year_index == 2012)) {
        //l is the variable for the number of days in the month from the array above ex:28, 30, 31
        for (var i = 0, l = calendar[month_index][1]; i < l + 1; i++) {
            //the first variable is what number will be displayed in the day drop down
            df.appendChild(createOption(i + 1, i));
        }
        clearChildren(sel_day);
        sel_day.appendChild(df);
    } else {}}  

    function generateMonths() {
        var df = document.createDocumentFragment();
        calendar.forEach(function(info, i) {
            df.appendChild(createOption(info[0], i));
        });
        //clears past months
        clearChildren(sel_month);
        //appends new months onto variable df
        sel_month.appendChild(df);
    }

    function generateYears() {
        var df = document.createDocumentFragment();
        years.forEach(function(i) {
            df.appendChild(createYearOption(i));
        });
        //clears past months
        clearChildren(sel_year);
        //appends new months onto variable df
        sel_year.appendChild(df);
    }

    //anytime the month selector is changed this calls the function to change the days
    sel_month.onchange = recalculateDays;
    sel_year.onchange = recalculateDays2(this);

    //i believe this automatically runs the months and days functions specifically for when first loading the page
    generateMonths();
    recalculateDays();
    generateYears();

    //this is what displays each of the individual drop downs after everything has been done to them
    cont.appendChild(sel_year);
    cont.appendChild(sel_month);
    cont.appendChild(sel_day);
}());
</script>
</body>
</html>
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1 Answer

  1. Editorial Team

    An easy way to check if a year is a leap year would be to prototype this into your code:

    Date.prototype.isLeapYear = function() {
    return (new Date(this.getFullYear(),1,29).getMonth() == 1);
};

    Then you could update your array with the proper number of days in February.

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