CODEWITHSUNDEEP
javascriptnode.jsdatedatetimetimezone
David Torres
David Torres

Reputation: 1767

How to tell JavaScript Date where to take TimezoneOffset from?

I am using new Date(<date-string>) and then .getTime() to pass date strings to milliseconds from 1970.

The problem is that the date strings does not contain the timezone on them. They are British, so the timezone will be GMT or GMT+1 depending on the date...

When I use this technique in the front-end (Chrome), or in the back-end (Node.js). The time zone taken is the British one (GMT or GMT+1 depending on the date). I assume that is taken from the OS.

However, when using a Node.js server which I have been told is configured to be in UTC... the timezone is always going to be GMT, leading to errors during the British Summer Time.

Is there any way to tell Date to take the timezone from the OS without changing the server configuration?

Example:

var aDate = new Date('2016-06-23 10:15:0');
var timestamp = aDate.getTime();

Just in case my explanation is not clear:

// Executed on 28-06-2016

// In the browser (in London)
new Date().getTimezoneOffset();                            // -60
new Date('28-06-2016 11:11:11').getTimezoneOffset();       // -60
new Date('28-01-2016 11:11:11').getTimezoneOffset();       // 0

// In the Node.js server I am forced to use, which is configured to use UTC
new Date().getTimezoneOffset();                            // 0
new Date('28-06-2016 11:11:11').getTimezoneOffset();       // 0
new Date('28-01-2016 11:11:11').getTimezoneOffset();       // 0

// Ideally, I would like to have the output I get in the browser when I run the code in the UTC Node.js server

Upvotes: 0

Views: 3695

Answers (2)

McMath
McMath

Reputation: 7178

I recommend using Moment Timezone for this, since this would be needlessly complicated to implement without a library. To get UTC in milliseconds from a given date in a given timezone, you can do this:

const moment = require('moment-timezone');

function londonTimeToUTC(dateString) {
  return moment.tz(dateString, 'DD-MM-YYYY HH:mm:ss', 'Europe/London').valueOf();
}

console.log(londonTimeToUTC('28-06-2016 11:11:11')); // 1467108671000
console.log(londonTimeToUTC('28-01-2016 11:11:11')); // 1453979471000

The second argument passed to moment.tz() is a format string, which is necessary if the date string is not in ISO format. The third argument is any valid timezone identifier.

Upvotes: 2

Matt Johnson-Pint
Matt Johnson-Pint

Reputation: 241959

Is there any way to tell Date to take the timezone from the OS without changing the server configuration?

The time zone from the OS is what the Date object uses. If you're asking if you can change that time zone without changing the configuration, then no - there is not a way to do that. The Date object always takes on the behavior of the local time zone. Even if you supply an offset in the input string, it just uses that to determine the internal UTC timestamp. Output via most of the properties (including toString and getTimezoneOffset) will always use the local time zone.

Even in your examples, you cannot count on the browser behavior always returning the values you showed, simply because each user visiting your web site may have a different time zone setting.

The recommended way to deal with this is by using the moment.js library, which can handle UTC and local time by itself, but may require use of the moment-timezone extension if you are wanting to work with a specific time zone, such as Europe/London.

Now, with that said, if you're certain that your entire node.js application will run in a single time zone, and you're running on Linux or OSX (not Windows), then you can indeed change which time zone that node.js considers to be "local". Simply set the TZ environment variable before you launch node, like this:

env TZ='Europe/London' node server.js

There is no equivalent for the browser, or for Windows. And you still have to contend with possible non-UK users on your web site - so this doesn't guaranteed a match between client and server time. But it does address your question.

See also:

Upvotes: 2

Related Questions