Determine timezone from lat/long in NodeJS

npm install tzwhere

var tzwhere = require('tzwhere')
tzwhere.init();

var whiteHouse = {'lat': 38.897663, 'lng': -77.036562};

// Determine the timezone of the White House
console.log(tzwhere.tzNameAt(whiteHouse['lat'], whiteHouse['lng']));

// Determine the current offset from UTC, in milliseconds, of the White House's timezone
console.log(tzwhere.tzOffsetAt(whiteHouse['lat'], whiteHouse['lng']));

yields:

America/New_York
-14400000

or

America/New_York
-18000000

depending on the current state of daylight savings time in the America/New_York timezone. You can also do it asynchronously.

...
tzwhere.tzNameAt(whiteHouse['lat'], whiteHouse['lng'], function (error, result) {
	if (error) {
		console.log(error);
	} else {
		console.log(result);
	}
}
...

If your queries are only within a certain region you can optimize the instantiation of this library by creating regional GeoJSON shape files from the one included.

var tzwhere = require('tzwhere')
tzwhere.createRegionalGEOJsonShapeFile( 'America' );

You will only need to do this once and then would include the regional GeoJSON file in your distributions. See the example below for how to use this file.

You can also pass alternative GeoJSON shape files:

var tzwhere = require('tzwhere')
tzwhere.init('path/to/alternative/tz/file');

...

Check the tests for more comprehensive usage, including determining the timezone offsets at arbitrary dates (very useful for scheduling future events expressed in local time).

tzwhere is free software, and is distributed under the terms of the MIT license (see LICENSE.txt).