The start of a week varies officially in different countries.

This is a plugin for the spacetime library, to help understand week-starts/ends, by country or timezone.

It does some opinionated guesswork to determine the most appropriate week-start, when a timezone is given.

It returns an english name of the day used in javascript.

npm i spacetime-week-start

import spacetime from 'spacetime'
import weekStart from 'spacetime-week-start'
spacetime.extend(weekStart)

let s = spacetime.now('Europe/Berlin')

// with no argument, it uses the timezone of the spacetime object
s.weekStart()
// { day: 'monday', country: 'germany' }

// or, look up a country by name
s.weekStart('canada')
// { day: 'sunday', country: 'canada' }

s.weekStart('iran')
// { day: 'saturday', country: 'iran' }

The weekStart method accepts one optional argument - the name of a country:

• you don't have to supply the full name of a country - part of the name is enough (f.e. instead of united states of america just united states, or a unique part of the name, like ted sta)
• the country name can be in any case (lower, upper, camel case)
• if the country lookup is successful, it returns a simple object:

s.weekStart('united states')
// { day: 'sunday', country: 'united states of america' }

• some timezones have general names, such as gmt, utc or zulu. These return:

spacetime.now('Etc/Zulu').weekStart()
// { day: 'monday', location: 'zulu' }

• if you supply a non-string, null, undefined, an unknown name, or no argument at all, it returns the first day of the week for the object's timezone

Used various sources to determine most accurate guess:

• First Day of the Week in Different Countries
• CLDR - Unicode Common Locale Data Repository
• CLDR - day and week data file
• Wikipedia - Workweek and weekend
• Time & Date
• Time zone converter

MIT