Intl.Locale.prototype.weekInfo

let he = new Intl.Locale("he");
console.log(he.weekInfo); // logs {firstDay: 7, weekend: [5, 6], minimalDays: 1}

let af = new Intl.Locale("af");
console.log(af.weekInfo); // logs  {firstDay: 7, weekend: [6, 7], minimalDays: 1}

let enGB = new Intl.Locale("en-GB");
console.log(enGB.weekInfo) // logs  {firstDay: 1, weekend: [6, 7], minimalDays: 4}

let msBN = new Intl.Locale("en-GB");
console.log(msBN.weekInfo) // logs {firstDay: 7, weekend: [5, 7], minimalDays: 1}  // Brunei weekend is Friday and Sunday but not Saturday