使用JavaScript和Moment.js从时间偏移猜测时区

Question

I know this is not going to be foolproof because an offset isn't specific to a timezone, but with location data it seems like it would be possible to make an educated guess.

Basically, I would like to be able to take an object similar to this:

{
  offset: -5,
  location: 'America'
}

...and get back either a single or multiple matching time zones, which would be:

['America/Montreal', 'America/New_York', ...]

One solution I can think of is iterating through the zone data provided by moment-timezone , but that just doesn't seem like an elegant way to get this info.

Any ideas?

Answer 1

It's not really elegant but iterating through the time zone database allows to get all timezones associated with a given offset.

Note that the timezone database stores the variation of offset due to the daylight saving rules and also the historical evolution of time zones.

Given an offset in minutes, this function returns, according to the iana timezone database , the list of all timezones that used this offset once in the history or that will use this offset once in the futur.

function getZonesByOffset(offset){
  //offset in minutes
  results = [];
  var tzNames = moment.tz.names();
  for(var i in tzNames){
    var zone = moment.tz.zone(tzNames[i]);
    for(var j in zone.offsets){
      if(zone.offsets[j] === offset){
        //Add the new timezone only if not already present
        var inside = false;
        for(var k in results){
          if(results[k] === tzNames[i]){
            inside = true;
          }
        }
        if(!inside){
          results.push(tzNames[i]);
        }
      }
    }
  }

Answer 2

moment-timezone@0.5.0 added moment.tz.guess() which attempts to guess the user's most likely timezone by looking at Date#getTimezoneOffset and Date#toString . It then picks the zone with the largest population. It's not perfect, but it's close enough! Data is pulled from this table and Intl is used when available.

Fiddle

moment.tz.guess()

//= America/New_York (I'm in America/Montreal, but this works too)