How Can I Determine If Week Starts On Monday Or Sunday Based On Locale In Pure Javascript?

Well, the title is pretty explanatory - I need to figure out the day week start in local - it can be Monday, Sunday, Saturday or Friday - in pure Javascript. I found this https://s

Solution 1:

Without moment. Essentially a heavily golfed version of https://github.com/gamtiq/weekstart, ignoring some unusual locales. No pure JS answer (using APIs available as of 2020) is going to be perfect, but this will yield the same result as a system API would for at least 99.9% of users.

https://github.com/tc39/proposal-intl-locale-info has been proposed which will include an API level solution for this.

functionweekStart(region, language) {
  const regionSat = 'AEAFBHDJDZEGIQIRJOKWLYOMQASDSY'.match(/../g);
  const regionSun = 'AGARASAUBDBRBSBTBWBZCACNCODMDOETGTGUHKHNIDILINJMJPKEKHKRLAMHMMMOMTMXMZNINPPAPEPHPKPRPTPYSASGSVTHTTTWUMUSVEVIWSYEZAZW'.match(/../g);
  const languageSat = ['ar','arq','arz','fa'];
  const languageSun = 'amasbndzengnguhehiidjajvkmknkolomhmlmrmtmyneomorpapssdsmsnsutatethtnurzhzu'.match(/../g);

  return (
    region ? (
      regionSun.includes(region) ? 'sun' :
      regionSat.includes(region) ? 'sat' : 'mon') : (
      languageSun.includes(language) ? 'sun' :
      languageSat.includes(language) ? 'sat' : 'mon'));
}

functionweekStartLocale(locale) {
  const parts = locale.match(/^([a-z]{2,3})(?:-([a-z]{3})(?=$|-))?(?:-([a-z]{4})(?=$|-))?(?:-([a-z]{2}|\d{3})(?=$|-))?/i);
  returnweekStart(parts[4], parts[1]);
}

console.log(weekStartLocale(navigator.language));
console.log(weekStartLocale('en'));
console.log(weekStartLocale('en-GB'));
console.log(weekStartLocale('ar-AE'));

Solution 2:

you could use moment.js

moment.localeData('en-us').firstDayOfWeek();

As for pure js, you would have to make your own lookup table. You can use momentjs source code for reference. https://github.com/moment/moment/tree/develop/locale

In each of each locale file look for the dow at the end of the config.