Matching multiple ordered candidates

[jamiebuilds-signal]

It is occasionally useful to be able to test if multiple locales are good candidates according a user's preferences. For example:

• Configuring spellcheckers for multiple languages.
• Display a locale <select> with the user's preferences hoisted to the top.

I will say it's totally possible to do this with just this API, it's just slightly involved:

let requestedLocales = ["fa-FR", "fr-FR"]
let availableLocales = ["en-US", "fr-FR", "fa-IR", "zh-Hans-CN"]
let defaultLocale = "en-US"
let options = { algorithm: "best fit" }
let fakeDefaultLocale = "en-x-ignore";

let matchedLocales = []

requestedLocales.forEach((requestedLocale) => {
  let match = Intl.LocaleMatcher.match(
    [requestedLocale], 
    availableLocales, 
    fakeDefaultLocale,
    options
  )
  if (match !== fakeDefaultLocale) {
    matchedLocales.push(match)
  }
})

if (matchedLocales.length === 0) {
  matchedLocales.push(defaultLocale)
}

// matchedLocales == ["fa-IR", "fr-FR"]

However, it seems like an easy thing to just bake into this API to make it more useful:

let matchedLocales = Intl.LocaleMatcher.matchMany(
  requestedLocales, 
  availableLocales, 
  defaultLocale,
  options
)
// matchedLocales == ["fa-IR", "fr-FR"]