Timezone America/Montevideo

Question

If I compute the current local time in Montevideo with the following code:

var dt = new Date().toLocaleString("en-US", {timeZone: "America/Montevideo"})
console.log(dt);

I get:

11/29/2015, 9:46:10 AM

If I check this time on the web, for instance with: http://www.zeitverschiebung.net/en/timezone/america--montevideo I get:

11/29/2015, 8:46:10 AM

Why is there 1h difference ?

Answer 1

The time zone rules for Uruguay changed in release 2015f of the IANA time zone data, which is probably what the web site is using - but I suspect your browser is still using relatively old time zone data.

Relevant rules in 2015e:

Rule    Uruguay 2006    max -   Oct Sun>=1   2:00   1:00    S
Rule    Uruguay 2007    max -   Mar Sun>=8   2:00   0   -

And equivalent in 2015f:

Rule    Uruguay 2006    2014    -   Oct Sun>=1   2:00   1:00    S
Rule    Uruguay 2007    2015    -   Mar Sun>=8   2:00   0   -

Basically, this means that from 2015 onwards, Uruguay doesn't observe daylight savings.

The notes read:

# From Steffen Thorsen (2015-06-30):
# ... it looks like they will not be using DST the coming summer:
# http://www.elobservador.com.uy/gobierno-resolvio-que-no-habra-cambio-horario-verano-n656787
# http://www.republica.com.uy/este-ano-no-se-modificara-el-huso-horario-en-uruguay/523760/
# From Paul Eggert (2015-06-30):
# Apparently restaurateurs complained that DST caused people to go to the beach
# instead of out to dinner.
# From Pablo Camargo (2015-07-13):
# http://archivo.presidencia.gub.uy/sci/decretos/2015/06/cons_min_201.pdf
# [dated 2015-06-29; repeals Decree 311/006 dated 2006-09-04]

Answer 2

This is actually a really interesting situation! This is clearly a daylight savings time issue. What happened is that the Uruguayan government decided to abolish daylight savings this year and it has caused a number of sites to become outdated as every year prior to this one, daylight savings started in October.

A very similar issue happened in Israel several years back when the government decided to change the announced DST date and it has caused a number of DST issues with automated systems for several weeks.

This is the announcement regarding Uruguay DST: http://www.elobservador.com.uy/gobierno-resolvio-que-no-habra-cambio-horario-verano-n656787