├── README
└── detect_timezone.js


/README:
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 1 | Makes a robust determination of a user's timezone through Javascript.
 2 | 
 3 | /* 
 4 |  * Original script by Josh Fraser (http://www.onlineaspect.com)
 5 |  * Continued by Jon Nylander, (jon at pageloom dot com)
 6 |  * Refactored to be more "library"-like by Rowan Crawford (wombleton at gmail punctuation com)
 7 |  * According to both of us, you are absolutely free to do whatever 
 8 |  * you want with this code.
 9 |  * 
10 |  * This code is  maintained at bitbucket.org as jsTimezoneDetect.
11 |  */
12 | 


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/detect_timezone.js:
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  1 | /*jslint indent: 2, nomen: false, white: false, plusplus: false, regexp: false */
  2 | /*global jQuery: false */
  3 | 
  4 | /*
  5 |  * Original script by Josh Fraser (http://www.onlineaspect.com)
  6 |  * Continued by Jon Nylander, (jon at pageloom dot com)
  7 |  * According to both of us, you are absolutely free to do whatever 
  8 |  * you want with this code.
  9 |  * 
 10 |  * This code is  maintained at bitbucket.org as jsTimezoneDetect.
 11 |  */
 12 | (function($) {var HEMISPHERE_SOUTH = 'SOUTH',
 13 |       HEMISPHERE_NORTH = 'NORTH',
 14 |       HEMISPHERE_UNKNOWN = 'N/A',
 15 |       olson = {};
 16 | 
 17 |   /**
 18 |    * A simple object containing information of utc_offset, which olson timezone key to use,
 19 |    * and if the timezone cares about daylight savings or not.
 20 |    *
 21 |    * @constructor
 22 |    * @param {string} offset - for example '-11:00'
 23 |    * @param {string} olson_tz - the olson Identifier, such as "America/Denver"
 24 |    * @param {boolean} uses_dst - flag for whether the time zone somehow cares about daylight savings.
 25 |    */
 26 |   function TimeZone(offset, olson_tz, uses_dst) {
 27 |     this.utc_offset = offset;
 28 |     this.olson_tz = olson_tz;
 29 |     this.uses_dst = uses_dst;
 30 |   }
 31 | 
 32 |   /**
 33 |    * Prints out the result.
 34 |    * But before it does that, it calls this.ambiguity_check.
 35 |    */
 36 |   TimeZone.prototype.display = function() {
 37 |     this.ambiguity_check();
 38 |     var response_text = '<b>UTC-offset</b>: ' + this.utc_offset + '<br/>';
 39 |     response_text += '<b>Olson database name</b>: ' + this.olson_tz + '<br/>';
 40 |     response_text += '<b>Daylight Savings</b>: ' + (this.uses_dst ? 'yes' : 'no') + '<br/>';
 41 | 
 42 |     return response_text;
 43 |   };
 44 | 
 45 |   /**
 46 |    * Gets the offset in minutes from UTC for a certain date.
 47 |    *
 48 |    * @param date
 49 |    * @returns {number}
 50 |    */
 51 |   function get_date_offset(date) {
 52 |     return -date.getTimezoneOffset();
 53 |   }
 54 | 
 55 |   function get_january_offset() {
 56 |     return get_date_offset(new Date(2011, 0, 1, 0, 0, 0, 0));
 57 |   }
 58 | 
 59 |   function get_june_offset() {
 60 |     return get_date_offset(new Date(2011, 5, 1, 0, 0, 0, 0));
 61 |   }
 62 | 
 63 |   /**
 64 |    * Checks whether a given date is in daylight savings time.
 65 |    *
 66 |    * If the date supplied is after june, we assume that we're checking
 67 |    * for southern hemisphere DST.
 68 |    *
 69 |    * @param {Date} date
 70 |    * @returns {boolean}
 71 |    */
 72 |   function date_is_dst(date) {
 73 |     var base_offset = ( (date.getMonth() > 5 ? get_june_offset() : get_january_offset()) ),
 74 |         date_offset = get_date_offset(date);
 75 | 
 76 |     return (base_offset - date_offset) !== 0;
 77 |   }
 78 | 
 79 |   /**
 80 |    * Checks if a timezone has possible ambiguities. I.e timezones that are similar.
 81 |    *
 82 |    * If the preliminary scan determines that we're in America/Denver. We double check
 83 |    * here that we're really there and not in America/Mazatlan.
 84 |    *
 85 |    * This is done by checking known dates for when daylight savings start for different
 86 |    * timezones.
 87 |    */
 88 |   TimeZone.prototype.ambiguity_check = function() {
 89 |     var i,
 90 |         local_ambiguity_list = olson.ambiguity_list[this.olson_tz],
 91 |         length,
 92 |         tz;
 93 | 
 94 |     if (typeof(local_ambiguity_list) === 'undefined') {
 95 |       return;
 96 |     }
 97 | 
 98 |     length = local_ambiguity_list.length;
 99 | 
100 |     for (i = 0; i < length; i++) {
101 |       tz = local_ambiguity_list[i];
102 | 
103 |       if (date_is_dst(olson.dst_start_dates[tz])) {
104 |         this.olson_tz = tz;
105 |         return;
106 |       }
107 |     }
108 |   };
109 | 
110 |   /**
111 |    * The keys in this dictionary are comma separated as such:
112 |    *
113 |    * First the offset compared to UTC time in minutes.
114 |    *
115 |    * Then a flag which is 0 if the timezone does not take daylight savings into account and 1 if it does.
116 |    *
117 |    * Thirdly an optional 's' signifies that the timezone is in the southern hemisphere, only interesting for timezones with DST.
118 |    *
119 |    * The values of the dictionary are TimeZone objects.
120 |    */
121 |   olson.timezones = {
122 |     '-720,0'   : new TimeZone('-12:00', 'Etc/GMT+12', false),
123 |     '-660,0'   : new TimeZone('-11:00', 'Pacific/Pago_Pago', false),
124 |     '-600,1'   : new TimeZone('-11:00', 'America/Adak', true),
125 |     '-660,1,s' : new TimeZone('-11:00', 'Pacific/Apia', true),
126 |     '-600,0'   : new TimeZone('-10:00', 'Pacific/Honolulu', false),
127 |     '-570,0'   : new TimeZone('-10:30', 'Pacific/Marquesas', false),
128 |     '-540,0'   : new TimeZone('-09:00', 'Pacific/Gambier', false),
129 |     '-540,1'   : new TimeZone('-09:00', 'America/Anchorage', true),
130 |     '-480,1'   : new TimeZone('-08:00', 'America/Los_Angeles', true),
131 |     '-480,0'   : new TimeZone('-08:00', 'Pacific/Pitcairn', false),
132 |     '-420,0'   : new TimeZone('-07:00', 'America/Phoenix', false),
133 |     '-420,1'   : new TimeZone('-07:00', 'America/Denver', true),
134 |     '-360,0'   : new TimeZone('-06:00', 'America/Guatemala', false),
135 |     '-360,1'   : new TimeZone('-06:00', 'America/Chicago', true),
136 |     '-360,1,s' : new TimeZone('-06:00', 'Pacific/Easter', true),
137 |     '-300,0'   : new TimeZone('-05:00', 'America/Bogota', false),
138 |     '-300,1'   : new TimeZone('-05:00', 'America/New_York', true),
139 |     '-270,0'   : new TimeZone('-04:30', 'America/Caracas', false),
140 |     '-240,1'   : new TimeZone('-04:00', 'America/Halifax', true),
141 |     '-240,0'   : new TimeZone('-04:00', 'America/Santo_Domingo', false),
142 |     '-240,1,s' : new TimeZone('-04:00', 'America/Asuncion', true),
143 |     '-210,1'   : new TimeZone('-03:30', 'America/St_Johns', true),
144 |     '-180,1'   : new TimeZone('-03:00', 'America/Godthab', true),
145 |     '-180,0'   : new TimeZone('-03:00', 'America/Argentina/Buenos_Aires,', false),
146 |     '-180,1,s' : new TimeZone('-03:00', 'America/Montevideo', true),
147 |     '-120,0'   : new TimeZone('-02:00', 'America/Noronha', false),
148 |     '-120,1'   : new TimeZone('-02:00', 'Etc/GMT+2', true),
149 |     '-60,1'    : new TimeZone('-01:00', 'Atlantic/Azores', true),
150 |     '-60,0'    : new TimeZone('-01:00', 'Atlantic/Cape_Verde', false),
151 |     '0,0'      : new TimeZone('00:00', 'Africa/Casablanca', false),
152 |     '0,1'      : new TimeZone('00:00', 'Europe/London', true),
153 |     '60,1'     : new TimeZone('+01:00', 'Europe/Berlin', true),
154 |     '60,0'     : new TimeZone('+01:00', 'Africa/Lagos', false),
155 |     '60,1,s'   : new TimeZone('+01:00', 'Africa/Windhoek', true),
156 |     '120,1'    : new TimeZone('+02:00', 'Asia/Beirut', true),
157 |     '120,0'    : new TimeZone('+02:00', 'Africa/Johannesburg', false),
158 |     '180,1'    : new TimeZone('+03:00', 'Europe/Moscow', true),
159 |     '180,0'    : new TimeZone('+03:00', 'Asia/Baghdad', false),
160 |     '210,1'    : new TimeZone('+03:30', 'Asia/Tehran', true),
161 |     '240,0'    : new TimeZone('+04:00', 'Asia/Dubai', false),
162 |     '240,1'    : new TimeZone('+04:00', 'Asia/Yerevan', true),
163 |     '270,0'    : new TimeZone('+04:30', 'Asia/Kabul', false),
164 |     '300,1'    : new TimeZone('+05:00', 'Asia/Yekaterinburg', true),
165 |     '300,0'    : new TimeZone('+05:00', 'Asia/Karachi', false),
166 |     '330,0'    : new TimeZone('+05:30', 'Asia/Kolkata', false),
167 |     '345,0'    : new TimeZone('+05:45', 'Asia/Kathmandu', false),
168 |     '360,0'    : new TimeZone('+06:00', 'Asia/Dhaka', false),
169 |     '360,1'    : new TimeZone('+06:00', 'Asia/Omsk', true),
170 |     '390,0'    : new TimeZone('+06:30', 'Asia/Rangoon', false),
171 |     '420,1'    : new TimeZone('+07:00', 'Asia/Krasnoyarsk', true),
172 |     '420,0'    : new TimeZone('+07:00', 'Asia/Jakarta', false),
173 |     '480,0'    : new TimeZone('+08:00', 'Asia/Shanghai', false),
174 |     '480,1'    : new TimeZone('+08:00', 'Asia/Irkutsk', true),
175 |     '525,0'    : new TimeZone('+08:45', 'Australia/Eucla', true),
176 |     '525,1,s'  : new TimeZone('+08:45', 'Australia/Eucla', true),
177 |     '540,1'    : new TimeZone('+09:00', 'Asia/Yakutsk', true),
178 |     '540,0'    : new TimeZone('+09:00', 'Asia/Tokyo', false),
179 |     '570,0'    : new TimeZone('+09:30', 'Australia/Darwin', false),
180 |     '570,1,s'  : new TimeZone('+09:30', 'Australia/Adelaide', true),
181 |     '600,0'    : new TimeZone('+10:00', 'Australia/Brisbane', false),
182 |     '600,1'    : new TimeZone('+10:00', 'Asia/Vladivostok', true),
183 |     '600,1,s'  : new TimeZone('+10:00', 'Australia/Sydney', true),
184 |     '630,1,s'  : new TimeZone('+10:30', 'Australia/Lord_Howe', true),
185 |     '660,1'    : new TimeZone('+11:00', 'Asia/Kamchatka', true),
186 |     '660,0'    : new TimeZone('+11:00', 'Pacific/Noumea', false),
187 |     '690,0'    : new TimeZone('+11:30', 'Pacific/Norfolk', false),
188 |     '720,1,s'  : new TimeZone('+12:00', 'Pacific/Auckland', true),
189 |     '720,0'    : new TimeZone('+12:00', 'Pacific/Tarawa', false),
190 |     '765,1,s'  : new TimeZone('+12:45', 'Pacific/Chatham', true),
191 |     '780,0'    : new TimeZone('+13:00', 'Pacific/Tongatapu', false),
192 |     '840,0'    : new TimeZone('+14:00', 'Pacific/Kiritimati', false)
193 |   };
194 | 
195 |   /**
196 |    * This object contains information on when daylight savings starts for
197 |    * different timezones.
198 |    *
199 |    * The list is short for a reason. Often we do not have to be very specific
200 |    * to single out the correct timezone. But when we do, this list comes in
201 |    * handy.
202 |    *
203 |    * Each value is a date denoting when daylight savings starts for that timezone.
204 |    */
205 |   olson.dst_start_dates = {
206 |     'America/Denver' : new Date(2011, 2, 13, 3, 0, 0, 0),
207 |     'America/Mazatlan' : new Date(2011, 3, 3, 3, 0, 0, 0),
208 |     'America/Chicago' : new Date(2011, 2, 13, 3, 0, 0, 0),
209 |     'America/Mexico_City' : new Date(2011, 3, 3, 3, 0, 0, 0),
210 |     'Atlantic/Stanley' : new Date(2011, 8, 4, 7, 0, 0, 0),
211 |     'America/Asuncion' : new Date(2011, 9, 2, 3, 0, 0, 0),
212 |     'America/Santiago' : new Date(2011, 9, 9, 3, 0, 0, 0),
213 |     'America/Campo_Grande' : new Date(2011, 9, 16, 5, 0, 0, 0),
214 |     'America/Montevideo' : new Date(2011, 9, 2, 3, 0, 0, 0),
215 |     'America/Sao_Paolo' : new Date(2011, 9, 16, 5, 0, 0, 0),
216 |     'America/Los_Angeles' : new Date(2011, 2, 13, 8, 0, 0, 0),
217 |     'America/Santa_Isabel' : new Date(2011, 3, 5, 8, 0, 0, 0),
218 |     'America/Havana' : new Date(2011, 2, 13, 2, 0, 0, 0),
219 |     'America/New_York' : new Date(2011, 2, 13, 7, 0, 0, 0),
220 |     'Asia/Gaza' : new Date(2011, 2, 26, 23, 0, 0, 0),
221 |     'Asia/Beirut' : new Date(2011, 2, 27, 1, 0, 0, 0),
222 |     'Europe/Minsk' : new Date(2011, 2, 27, 3, 0, 0, 0),
223 |     'Europe/Istanbul' : new Date(2011, 2, 27, 7, 0, 0, 0),
224 |     'Asia/Damascus' : new Date(2011, 3, 1, 2, 0, 0, 0),
225 |     'Asia/Jerusalem' : new Date(2011, 3, 1, 6, 0, 0, 0),
226 |     'Africa/Cairo' : new Date(2011, 3, 29, 4, 0, 0, 0),
227 |     'Asia/Yerevan' : new Date(2011, 2, 27, 4, 0, 0, 0),
228 |     'Asia/Baku'    : new Date(2011, 2, 27, 8, 0, 0, 0),
229 |     'Pacific/Auckland' : new Date(2011, 8, 26, 7, 0, 0, 0),
230 |     'Pacific/Fiji' : new Date(2010, 11, 29, 23, 0, 0, 0),
231 |     'America/Halifax' : new Date(2011, 2, 13, 6, 0, 0, 0),
232 |     'America/Goose_Bay' : new Date(2011, 2, 13, 2, 1, 0, 0),
233 |     'America/Miquelon' : new Date(2011, 2, 13, 5, 0, 0, 0),
234 |     'America/Godthab' : new Date(2011, 2, 27, 1, 0, 0, 0)
235 |   };
236 | 
237 |   /**
238 |    * The keys in this object are timezones that we know may be ambiguous after
239 |    * a preliminary scan through the olson_tz object.
240 |    *
241 |    * The array of timezones to compare must be in the order that daylight savings
242 |    * starts for the regions.
243 |    */
244 |   olson.ambiguity_list = {
245 |     'America/Denver' : ['America/Denver','America/Mazatlan'],
246 |     'America/Chicago' : ['America/Chicago','America/Mexico_City'],
247 |     'America/Asuncion' : ['Atlantic/Stanley', 'America/Asuncion', 'America/Santiago','America/Campo_Grande'],
248 |     'America/Montevideo' : ['America/Montevideo', 'America/Sao_Paolo'],
249 |     'Asia/Beirut' : ['Asia/Gaza','Asia/Beirut', 'Europe/Minsk', 'Europe/Istanbul', 'Asia/Damascus', 'Asia/Jerusalem','Africa/Cairo'],
250 |     'Asia/Yerevan' : ['Asia/Yerevan', 'Asia/Baku'],
251 |     'Pacific/Auckland' : ['Pacific/Auckland', 'Pacific/Fiji'],
252 |     'America/Los_Angeles' : ['America/Los_Angeles', 'America/Santa_Isabel'],
253 |     'America/New_York' : ['America/Havana','America/New_York'],
254 |     'America/Halifax' : ['America/Goose_Bay','America/Halifax'],
255 |     'America/Godthab' : ['America/Miquelon', 'America/Godthab']
256 |   };
257 | 
258 | 
259 |   /**
260 |    * This function does some basic calculations to create information about
261 |    * the user's timezone.
262 |    *
263 |    * Returns a primitive object on the format
264 |    * {'utc_offset' : -9, 'dst': 1, hemisphere' : 'north'}
265 |    * where dst is 1 if the region uses daylight savings.
266 |    *
267 |    * @returns {Object}
268 |    */
269 |   function get_timezone_info() {
270 |     var january_offset = get_january_offset(),
271 |         june_offset = get_june_offset(),
272 |         diff = january_offset - june_offset;
273 | 
274 |     if (diff < 0) {
275 |       return {'utc_offset' : january_offset,
276 |         'dst':  1,
277 |         'hemisphere' : HEMISPHERE_NORTH};
278 |     }
279 |     else if (diff > 0) {
280 |       return {'utc_offset' : june_offset,
281 |         'dst' : 1,
282 |         'hemisphere' : HEMISPHERE_SOUTH};
283 |     }
284 | 
285 |     return {'utc_offset' : january_offset,
286 |       'dst': 0,
287 |       'hemisphere' : HEMISPHERE_UNKNOWN};
288 |   }
289 | 
290 |   /**
291 |    * Uses get_timezone_info() to formulate a key to use in the olson.timezones dictionary.
292 |    *
293 |    * Returns a primitive object on the format:
294 |    * {'timezone': TimeZone, 'key' : 'the key used to find the TimeZone object'}
295 |    *
296 |    * @returns Object
297 |    */
298 |   function determine_timezone() {
299 |     var timezone_key_info = get_timezone_info(),
300 |         hemisphere_suffix = '',
301 |         tz_key;
302 | 
303 |     if (timezone_key_info.hemisphere === HEMISPHERE_SOUTH) {
304 |       hemisphere_suffix = ',s';
305 |     }
306 | 
307 |     tz_key = timezone_key_info.utc_offset + ',' + timezone_key_info.dst + hemisphere_suffix;
308 | 
309 |     return {
310 |       'timezone' : olson.timezones[tz_key],
311 |       'key' : tz_key,
312 |       name: olson.timezones[tz_key].olson_tz
313 |     };
314 |   }
315 | 
316 |   if ($ && $.extend) {
317 |     $.extend({
318 |       timezone: determine_timezone
319 |     });
320 |   } else {
321 |     jsDetectTimezone = {
322 |       timezone: determine_timezone
323 |     };
324 |   }
325 | }(jQuery));
326 | 


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