Formatting date and time - JavaScript

>> var mystartdate = new Date(startparts[2] + "-" + startparts[1] + "-" + startparts[0]);
Change that to:

var mystartdate = startparts[2] + "-" + startparts[1] + "-" + startparts[0];

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just concatenate the date parts.

You can try something like this - however your sample date is incorrect. If you are going to use that format for date it should be mm/dd/yyyy. Consider 04/04/2015 - it is ambiguous as to what is the month and what is the day. Convention is if you use forward slashes it is US format of m/d/y and if you use - (hyphens) it is UTC (y-m-d).

This code formats the date as you want it - you can modify it as needed.

Date.prototype.ymd= function()
{
    return this.getFullYear().toString() +
        "-" +
        (("00" + (this.getMonth() +1)).substr(-2)) + "-" +
        (("00" + this.getDate()).substr(-2));
};

var testdate = new Date("03/27/2015");
alert(testdate.ymd());

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Sample here

Ahhh - thanks that worked (so easy when you know how) - I'm wondering if I just made a new problem for myself though...

you'll see from the code below that I am trying to reformat two datetimes to calc the duration in hh:mm between the two; I get a 'difference' result of NaN - presumably because these are now just strings - is there a solution?

var startdate = document.getElementById('<%=TxtStartDate.ClientID%>').value;
            var enddate = document.getElementById('<%=TxtEndDate.ClientID%>').value;
            
            var starthours = document.getElementById('<%=DDLStartHrs.ClientID%>').value;
            var startmins = document.getElementById('<%=DDLStartMins.ClientID%>').value;
            
            var endhours = document.getElementById('<%=DDLStopHrs.ClientID%>').value;
            var endmins = document.getElementById('<%=DDLStopMins.ClientID%>').value;
           

            var startparts = startdate.split('/');
            var endparts = enddate.split('/');
            

            var mystartdate = startparts[2] + "-" + startparts[1] + "-" + startparts[0];
            var myenddate = endparts[2] + "-" + endparts[1] + "-" + endparts[0];
            //var myenddate = new Date(endparts[2] + "-" + endparts[1] + "-" + endparts[0]);
            //var UTCstart = mystartdate.toUTCString();
            //var UTCend = myenddate.toUTCString();
            var started = (mystartdate + 'T' + starthours + ':' + startmins + ':00.000Z')
            var ended = (myenddate + 'T' + endhours + ':' + endmins + ':00.000Z');
            var difference = (ended - started) / (1000 * 3600);
            
            if (startdate != '') {
                document.getElementById('<%=Txttest1.ClientID%>').value = started;
                
            }

            if (enddate != '') {
                document.getElementById('<%=Txttest2.ClientID%>').value = ended;
            }

            if (startdate != '' && enddate != '') {
                document.getElementById('<%=Txttest3.ClientID%>').value = difference;
            }

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hi Julian,

I take your point re. date format but dd/mm/yyyy is the format generated by the calendar control.
Struggling to follow your example - sorry maybe my reply to hielo will clarify where I'm at..

Here is a documented version.

// EXTEND THE DATE OBJECT BY ADDING A NEW FUNCTION
// CALLED ymd
Date.prototype.ymd= function()
{
    // RETURN A STRING MADE UP OF 
    // THE FULL YEAR CONCATENATED TO ...

    return this.getFullYear().toString() +

    // THE SEPARATOR, CONCATENATED TO ...
        "-" +
    // THE MONTH. A SIMPLE TRICK TO GET 0 PADDED STRING
    // CONCATENATE THE MONTH (WHICH IS ZERO BASED
    // SO WE HAVE TO ADD 1) AND THEN TAKE THE RIGHT 2
    // CHAR'S  CONCATENATED TO ...
        (("00" + (this.getMonth() +1)).substr(-2)) + 

    // THE SEPARATOR, CONCATENATED TO ...
        "-" +

    // THE DAY. getDate RETURNS THE DAY (1-31)AND WE USE THE SAME 
    // TRICK FOR PADDING WITH ZERO'S
        (("00" + this.getDate()).substr(-2));
};

// CREATE A NEW DATE
var testdate = new Date("03/27/2015");

// OUTPUT IT IN yyyy-mm-dd FORMAT WITH THE NEW FUNCTION
alert(testdate.ymd());

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>> var difference = (ended - started) / (1000 * 3600);
What "difference" type are you looking for? Just hours?  what if it exceeds 24?

thanks both- I am looking for a 'difference' of hh:mm - it will not exceed 24hrs in this scenario.

fab thanks so much - that's working