javascript dates converted to bst time on android devices when using Firefox - javascript

I have a web application that runs on Chrome without any problems on a Android Device but when running it on Firefox it converts the "newvalue" to BST time zone instead of GMT Standard Time.
var now = new Date();
var start = new Date();
var newvalue = new Date(now - start);
The newvalue timezone output is GMT+0100(BST) but should actually be GMT+0000(GMT Standard Time)
Firefox is adding an an extra hour.
I have tried to convert to UTC and GMT but doesn't seem to work.
Any ideas?

OK so ... Ermmm ... I'm not clear on what you're doing with the line:
var newvalue = new Date(now - start);
Are you trying to time something?
Regardless, the first thing this line does is to subtract start from now, and give the difference between the 2 dates in milliseconds. Assuming this happens basically instantly, the result will be approximately (if not precisely) 0 milliseconds.
When you create a date and pass in a single parameter like this, you are asking for the date as it was, X milliseconds after epoch. Epoch is defined as Thursday Jan 1st 1970 (for reasons I won't go into). So by creating a new Date with a parameter of 0, you're just asking the browser to give you epoch.
Why Firefox decides to give you epoch in BST instead of GMT, I'll grant is actually pretty odd (since Jan 1st is clearly not in British Summer Time). But this fact is probably irrelevant, given that this is almost certainly NOT what you are trying to achieve here. If you're trying to time something, I'd suggest you probably just want to do:
var newvalue = start - now;
Where newvalue is now the difference in time. Note: I have swapped now and start around, since in your example start is defined after now, and hence this will give you the positive time difference.
EDIT IN RESPONSE TO COMMENT
To be clear, I'm suggesting that you DON'T create a new Date object with the result of the subtraction.
If you want to get the number of milliseconds between the two times using dates, just subtract them:
var start = new Date();
// do time consuming stuff
var end = new Date();
var difference = end - start; // NOT: var difference = new Date(end - start)

Resolved the issue by turning the two dates in to a UTC date and then finding the difference between the two dates using milliseconds.
This then works on Android.
Thanks for your assistance

Related

Set date() to midnight in users timezone with moment.js

I use moment.js to display a UTC date in the users local timezone:
var date = new Date(Date.UTC(2016,03,30,0,0,0));
var now = new Date();
var diff = (date.getTime()/1000) - (now.getTime()/1000);
var textnode = document.createTextNode(moment(date).format('dddd, DD.MM.YYYY') + ' a las ' + moment(date).format('HH:mm A'));
document.getElementsByClassName("date")[0].appendChild(textnode.cloneNode(true));
I later use the diff variable to show a countdown timer.
I would like to show a different countdown timer to everyone in their local time zone. (Using the difference till its midnight in their time zone, not in UTC)
But I am struggeling to get it work. Instead of using var date = new Date(Date.UTC(2016,03,30,0,0,0)); I probably need to use some function of moment.js that gives me till midnight in the users time zone.
The best example would be new years eve. If I use UTC everyone would have the same counter (9 hours left) but in different parts of the world this wouldn't make sense. For someone in australia it should be 2 hours left, and for someone in the US 14 hours.
I'm not sure that I fully understand your question, but I'll give you some general advice and tips.
When using moment.js, there is very little need to ever use the Date object. Only use it for interacting with other APIs that expect a Date object.
To get a moment in UTC, just use moment.utc(...), passing the appropriate arguments, such as moment.utc([2016,3,30]) or moment.utc('2016-04-30') for midnight April 30th UTC.
If you want to convert that back to the user's local time, use the .local() function. For example, moment.utc('2016-04-30').local() will create a moment with the equivalent local time to the UTC time provided.
If you want a moment in the user's local time, then that would be moment(...), such as moment([2016,3,30]) or moment('2016-04-30') for midnight April 30th local time.
You can difference two moments using the diff function, which can give the answer in specific units, such as m1.diff(m2, 'seconds') where m1 and m2 are moment objects.
You don't need to call format twice. Just encapsulate any text you want outputed with square brackets. .format('dddd, DD.MM.YYYY [a las] HH:mm A')
You might look into moment's locale support. If I'm not mistaken, "a las" indicates Spanish, however it's not always "a las", but sometimes "a la", if the hour is 1. Also, moment only uses those words in its .calendar() function, such as when producing a phrase like "mañana a las 13:17". A regular date formatted with .format('LLLL') in the Spanish locale would be something like: "sábado, 19 de marzo de 2016 13:17". So, you might want to verify that "a las" is exactly what you want in every case.
The title to this question was how to set a date to midnight. For that, I recommend using moment's startOf function. m.startOf('day') will give set the moment m to the start of the day, which is usually midnight. Keep in mind that not every local day actually starts at midnight in every time zone. Due to anomalies like daylight saving time, some days might start at 1:00. For example, this occurs in Brazil on October 16th this year.
Also, if you created the moment in UTC mode, you may wish to convert it back to local mode first before setting it to the start of the day. If you don't want to change the original moment object, be sure to clone it first.
Putting this all together:
var m1 = moment.utc([2016,3,30]);
var m2 = m1.clone().local().startOf('day');
var now = moment();
var diff = m1.diff(now, 'seconds');

Want to get Timezone using jquery

In jquery,
var date = new Date();
It is taking system Date Not site Time zone
var date = (new Date()).getTimezoneOffset();
it is also not working.please anyone help for this.thank you.
Return the timezone difference between UTC and Local Time:
var d = new Date()
var n = d.getTimezoneOffset();
The result n will be:
-300
The getTimezoneOffset() method returns the time difference between UTC time and local time, in minutes.
For example, If your time zone is GMT+2, -120 will be returned.
Note: The returned value is not a constant, because of the practice of using Daylight Saving Time.
Tip: The Universal Coordinated Time (UTC) is the time set by the World Time Standard.
Note: UTC time is the same as GMT time.
jQuery has only one date/time function, which is $.now()
If you meant JavaScript, the answer is still no. You can only obtain a time zone offset from date.getTimezoneOffset(). You can't get a time zone - at least not in all browsers.
You can guess at the time zone, by using the jsTimeZoneDetect library, but it is just a guess. It may or may not be accurate.
If you can guarantee your users are running a browser that supports the brand new ECMAScript Internationalization API, you can get the user's time zone with:
Intl.DateTimeFormat().resolvedOptions().timeZone

How to read the correct time/duration values from Google Spreadsheet

I'm trying to get from a time formatted Cell (hh:mm:ss) the hour value, the values can be bigger 24:00:00 for example 20000:00:00 should give 20000:
Table:
if your read the Value of E1:
var total = sheet.getRange("E1").getValue();
Logger.log(total);
The result is:
Sat Apr 12 07:09:21 GMT+00:09 1902
Now I've tried to convert it to a Date object and get the Unix time stamp of it:
var date = new Date(total);
var milsec = date.getTime();
Logger.log(Utilities.formatString("%11.6f",milsec));
var hours = milsec / 1000 / 60 / 60;
Logger.log(hours)
1374127872020.000000
381702.1866722222
The question is how to get the correct value of 20000 ?
Expanding on what Serge did, I wrote some functions that should be a bit easier to read and take into account timezone differences between the spreadsheet and the script.
function getValueAsSeconds(range) {
var value = range.getValue();
// Get the date value in the spreadsheet's timezone.
var spreadsheetTimezone = range.getSheet().getParent().getSpreadsheetTimeZone();
var dateString = Utilities.formatDate(value, spreadsheetTimezone,
'EEE, d MMM yyyy HH:mm:ss');
var date = new Date(dateString);
// Initialize the date of the epoch.
var epoch = new Date('Dec 30, 1899 00:00:00');
// Calculate the number of milliseconds between the epoch and the value.
var diff = date.getTime() - epoch.getTime();
// Convert the milliseconds to seconds and return.
return Math.round(diff / 1000);
}
function getValueAsMinutes(range) {
return getValueAsSeconds(range) / 60;
}
function getValueAsHours(range) {
return getValueAsMinutes(range) / 60;
}
You can use these functions like so:
var range = SpreadsheetApp.getActiveSheet().getRange('A1');
Logger.log(getValueAsHours(range));
Needless to say, this is a lot of work to get the number of hours from a range. Please star Issue 402 which is a feature request to have the ability to get the literal string value from a cell.
There are two new functions getDisplayValue() and getDisplayValues() that returns the datetime or anything exactly the way it looks to you on a Spreadsheet. Check out the documentation here
The value you see (Sat Apr 12 07:09:21 GMT+00:09 1902) is the equivalent date in Javascript standard time that is 20000 hours later than ref date.
you should simply remove the spreadsheet reference value from your result to get what you want.
This code does the trick :
function getHours(){
var sh = SpreadsheetApp.getActiveSpreadsheet();
var cellValue = sh.getRange('E1').getValue();
var eqDate = new Date(cellValue);// this is the date object corresponding to your cell value in JS standard
Logger.log('Cell Date in JS format '+eqDate)
Logger.log('ref date in JS '+new Date(0,0,0,0,0,0));
var testOnZero = eqDate.getTime();Logger.log('Use this with a cell value = 0 to check the value to use in the next line of code '+testOnZero);
var hours = (eqDate.getTime()+ 2.2091616E12 )/3600000 ; // getTime retrieves the value in milliseconds, 2.2091616E12 is the difference between javascript ref and spreadsheet ref.
Logger.log('Value in hours with offset correction : '+hours); // show result in hours (obtained by dividing by 3600000)
}
note : this code gets only hours , if your going to have minutes and/or seconds then it should be developped to handle that too... let us know if you need it.
EDIT : a word of explanation...
Spreadsheets use a reference date of 12/30/1899 while Javascript is using 01/01/1970, that means there is a difference of 25568 days between both references. All this assuming we use the same time zone in both systems. When we convert a date value in a spreadsheet to a javascript date object the GAS engine automatically adds the difference to keep consistency between dates.
In this case we don't want to know the real date of something but rather an absolute hours value, ie a "duration", so we need to remove the 25568 day offset. This is done using the getTime() method that returns milliseconds counted from the JS reference date, the only thing we have to know is the value in milliseconds of the spreadsheet reference date and substract this value from the actual date object. Then a bit of maths to get hours instead of milliseconds and we're done.
I know this seems a bit complicated and I'm not sure my attempt to explain will really clarify the question but it's always worth trying isn't it ?
Anyway the result is what we needed as long as (as stated in the comments) one adjust the offset value according to the time zone settings of the spreadsheet. It would of course be possible to let the script handle that automatically but it would have make the script more complex, not sure it's really necessary.
For simple spreadsheets you may be able to change your spreadsheet timezone to GMT without daylight saving and use this short conversion function:
function durationToSeconds(value) {
var timezoneName = SpreadsheetApp.getActive().getSpreadsheetTimeZone();
if (timezoneName != "Etc/GMT") {
throw new Error("Timezone must be GMT to handle time durations, found " + timezoneName);
}
return (Number(value) + 2209161600000) / 1000;
}
Eric Koleda's answer is in many ways more general. I wrote this while trying to understand how it handles the corner cases with the spreadsheet timezone, browser timezone and the timezone changes in 1900 in Alaska and Stockholm.
Make a cell somewhere with a duration value of "00:00:00". This cell will be used as a reference. Could be a hidden cell, or a cell in a different sheet with config values. E.g. as below:
then write a function with two parameters - 1) value you want to process, and 2) reference value of "00:00:00". E.g.:
function gethours(val, ref) {
let dv = new Date(val)
let dr = new Date(ref)
return (dv.getTime() - dr.getTime())/(1000*60*60)
}
Since whatever Sheets are doing with the Duration type is exactly the same for both, we can now convert them to Dates and subtract, which gives correct value. In the code example above I used .getTime() which gives number of milliseconds since Jan 1, 1970, ... .
If we tried to compute what is exactly happening to the value, and make corrections, code gets too complicated.
One caveat: if the number of hours is very large say 200,000:00:00 there is substantial fractional value showing up since days/years are not exactly 24hrs/365days (? speculating here). Specifically, 200000:00:00 gives 200,000.16 as a result.

Set JavaScript countdown to end at midnight PST?

I am trying to get a countdown to end Monday # midnight PST. I thought I had it working a week ago but apparently not.
I am using date.js
var monday = Date.today().next().monday();
var UTCmonday = new Date(monday.getTime() + monday.getTimezoneOffset() * 60000);
var PSTmonday = new Date(UTCmonday.setHours(UTCmonday.getHours() + 9));
$('#defaultCountdown').countdown({until: UTCmonday});
I think the problem is in determining UTC time? Am I right? How do I work this out?
Assuming you Pacific Standard Time, then you need to remember that PST === UTC-8
Thus, your third line would be
var PSTmonday = new Date(UTCmonday.setHours(UTCmonday.getHours() - 8));
The problem with this is that this will fail if the UTC is any earlier than 8am, since you can't pass a negative number into setHours.
Since you're using Datejs, why not use its full capabilities for changing the timezone?
http://code.google.com/p/datejs/wiki/APIDocumentation#setTimezone
Getting the time strictly in PST doesn't make much sense, as for almost half of the year PST isn't observed in the Pacific time zone. PST (UTC-8) is observed in the winter, and PDT (UTC-7) is observed in the summer. You can't represent Pacific Time as just a fixed offset, and unless it happens to be your own local time zone, you can't easily determine the transition between them without a time zone database. See the timezone tag wiki.
Also, date.js has been abandoned. I can't recommend any solution that continues its use. Support for the setTimezone method that Dancrumb suggested is culture specific, and it still doesn't take daylight saving time into consideration.
Instead, I recommend trying moment.js. You can use the moment-timezone add-on to work with the America/Los_Angeles zone - which is a good exemplar of US Pacific time. Make sure your moment-timezone-data.js file includes at least this zone. Then you can do the following:
var m = moment().tz('America/Los_Angeles').day(7).startOf('day');
var s = m.toISOString(); // if you need a string output representing UTC
var dt = m.toDate(); // if you need an actual JavaScript Date object
Let's break that down a bit:
moment() gets you the current time
tz('America/Los_Angeles') adjusts the time to the timezone you are interested in.
day(7) advances the time to the next Monday.
startOf('day') snaps the time back to midnight.

19 hour offset when setting moment to 0 (using moment.js)

Solved my own problem. I wanted to convert seconds to HH:mm:ss using moment.js. I used the following code, which worked, but I didn't know why moment(0) was setting the time of day to 19 00
var yearZero = moment(0).subtract('hours',19); //beginning of time
var sTimecode = yearZero.add('seconds', secondsUntilEvent).format("HH:mm:ss");
From http://momentjs.com/docs/#/parsing/unix-offset/
moment(Number);
Similar to new Date(Number), you can create a moment by passing an integer value representing the number of milliseconds since the Unix Epoch (Jan 1 1970 12AM UTC).
Didn't see anything about starting at 7PM / 19 00 there
The problem was that I was outputting it without declaring UTC. The following change did the trick:
var sTimecode = moment(0).add('seconds', secondsUntilEvent).utc().format("HH:mm:ss");
Perhaps someone else encountered the same problem (or not). Good day!
Instead of doing such a complicated workaround, you can always use the moment constructor to read an integer, which is interpreted as the number of milliseconds from the unix epoch. This works fine for me:
var value = moment(18000 * 1000).format('HH:mm:ss'); // 5 Hours
document.getElementById('date').innerHTML = value;
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.10.6/moment.min.js"></script>
<pre id="date"></pre>
Obviously, the time is displayed accordingly to your browser's timezone

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