JS Time difference problem

[r243]

Hi guys,
I'm developing a browser-based game which requires a javascript countdown.
I have one that works perfectly almost all the time, but I and several players have noticed times when it fails.

I think I have isolated the problem to midnight shifting. I have the following code, which generates the time difference between two dates in seconds:

date1 = (new Date(8, 10, 31, 20, 55, 0)).getTime();
date2 = (new Date(8, 10, 31, 23, 59, 0)).getTime();

Time_Left = Math.round((date2 - date1) / 1000);
 
alert(date2 + " - " + date1 + " = " + Time_Left);

This works fine. However, if I change date1 and date2 to i.e.

date1 = (new Date(8, 10, 31, 23, 55, 25)).getTime();
date2 = (new Date(8, 11, 1, 23, 59, 0)).getTime();

Time_Left will be a negative number even though it should be positive. I'm sure it's something really simple, but I can't see what. Anyone spot the problem?

Thanks

[glenngv]

Returns positive for me => 215000

It shouldn't be a problem as getTime() returns the number of milliseconds since midnight of 01/01/1970

[Philip M]

The year in the new Date() object should be 2008, not 8 which is interpreted as 1908, giving negative numbers of milliseconds.

But:-

date1 = (new Date(2008, 10, 31, 23, 55, 25)).getTime();
is invalid as month 10 (November) does not have 31 days. Months in Javascript are 0-11. Month 10 Day 31 is treated as Month 11 (December) Day 1 which explains why

date1 = (new Date(8, 10, 31, 20, 55, 0)).getTime();
date2 = (new Date(8, 10, 31, 23, 59, 0)).getTime();

returns a (negative!) value, but not the desired value.


You can check the validity of a date i.e. that the date exists (which in your case is strongly recommended) as follows:-

<script type = "text/javascript">

function checkValidDate() {
var yr = "2008";
var mm = "10";   //  mm = 0 - 11
var dd = "31"
var nd = new Date();
nd.setFullYear(yr,mm,dd);  // YYYY,MM(0-11),DD
var ndmm = nd.getMonth();
if (ndmm != mm) {
alert (dd + "/" + mm + "/" + yr  + " is an Invalid Date!");
return false; 
}
}

</script>

This checks to see if Javascript has adjusted the month value, and if so the date is not valid.


111,111,111 x 111,111,111 = 12,345,678,987,654,321

[r243]

Wonderful, thank you Philip!
The code example I posted before works now. Unfortunatley, it seems that my full script already compensates for this, and the year. (i didn't write the script myself, only modified it for my needs)

The dates are dynamically generated in asp. If target month is wrong then the time difference always would be wrong, right? And it works almost all the time.
This is my script:

function countdown_clock(year, month, day, hour, minute, second, format, divid)
	 {
		 html_code = '<div id="' + divid + '"></div>';
		 document.write(html_code);

		 Today = new Date();
		 Todays_Year = Today.getYear() - 2000;
		 Todays_Month = Today.getMonth() + 1;

		 <%
		 time_of_day = time
		 time_of_day = TimeValue(time_of_day)

		 today = date
		 today = DateValue(today)

		 current_second = second(time_of_day)
		 current_minute = minute(time_of_day)
		 current_hour = hour(time_of_day)
		 current_day = day(today)
		 current_month = month(today)    
		 current_year = year(today)                                             
		 %>

		 //Computes the time difference between the client computer and the server.
		 Server_Date = (new Date(<%= current_year - 2000 %>, <%= current_month %>, <%= current_day %>,
								 <%= current_hour %>, <%= current_minute %>, <%= current_second %>)).getTime();
		 Todays_Date = (new Date(Todays_Year, Todays_Month, Today.getDate(),
								 Today.getHours(), Today.getMinutes(), Today.getSeconds())).getTime();

		 countdown(year, month, day, hour, minute, second, (Todays_Date - Server_Date), format, divid);                
	 }

function countdown(year, month, day, hour, minute, second, time_difference, format, divid)
	 {
		 Today = new Date();
		 Todays_Year = Today.getYear() - 2000;
		 Todays_Month = Today.getMonth() + 1;

		 //Convert today's date and the target date into miliseconds.

		 Todays_Date = (new Date(Todays_Year, Todays_Month, Today.getDate(), Today.getHours(), Today.getMinutes(), Today.getSeconds())).getTime();
		 Target_Date = (new Date(year, month, day, hour, minute, second)).getTime();

		 //Find their difference, and convert that into seconds.
		 //Taking into account the time differential between the client computer and the server.
		   Time_Left = Math.round((Target_Date - Todays_Date + time_difference) / 1000);

		 if(Time_Left < 0)
			Time_Left = 0;

		//Output: HH:MM:SS
		hours = Math.floor(Time_Left / (60 * 60));
		Time_Left %= (60 * 60);
		minutes = Math.floor(Time_Left / 60);
		Time_Left %= 60;
		seconds = Time_Left;
		days=0;
		//No single numbers
		if(hours < 10) hours ='0' + hours;
		if(minutes < 10) minutes ='0' + minutes;
		if(seconds < 10) seconds ='0' + seconds;

		document.getElementById(divid).innerHTML = '';
		document.getElementById(divid).innerHTML += hours + ':';
		document.getElementById(divid).innerHTML += minutes + ':';
		document.getElementById(divid).innerHTML += seconds;

		 //Recursive call, keeps the clock ticking.
		 setTimeout('countdown(' + year + ',' + month + ',' + day + ',' + hour + ',' + minute + ',' + second + ',' + time_difference + ', ' + format + ', ' + divid + ');', 1000);
	 }

The only dates I know for sure didn't work were:

Todays_Date: 08, 10, 31, 23, 55, 0
Target_Date: 08, 11, 1, 0, 5, 0

Somehow this returned a negative number. I would be most grateful if you could pinpoint the error.

thank you again,
henrik

[Philip M]

Please read post #3. Was there something in that which is not clear?

One more time:-

Todays_Date: 08, 10, 31, 23, 55, 0
There is no 31st November. OK?

[r243]

Sorry, I did not mean that literally. At the time I noticed the error, it was about 23:55 the 31'st of october. And Todays_Date was generated, at that time, with this script:

Todays_Date = (new Date(Todays_Year, Todays_Month, Today.getDate(), Today.getHours(), Today.getMinutes(), Today.getSeconds())).getTime();

[Philip M]

If target month is wrong then the time difference always would be wrong, right?
No, wrong. Any month with less than 31 days will give an incorrect result if the 31st is selected (or of course >28 in February).

And it works almost all the time.
That means that it does not work. Period. You cannot be "almost a virgin".

Try changing Todays_Month to Todays_Month-1 (to change months 1-12 to 0-11)