in javascript/widgets/config.js [510:525]
getPhoneAuthDefaultCountry() {
const signInOptions = this.getSignInOptionsForProvider_(
firebase.auth.PhoneAuthProvider.PROVIDER_ID);
const iso2 = signInOptions && signInOptions['defaultCountry'] || null;
const countries = iso2 && country.getCountriesByIso2(iso2);
// Check if loginHint passed. If so, get the country ID from there.
// If no defaultCountry passed, use this value instead.
let defaultPhoneNumber = null;
if (signInOptions && typeof (signInOptions['loginHint']) === 'string') {
defaultPhoneNumber = PhoneNumber.fromString(
/** @type {string} */ (signInOptions['loginHint']));
}
// If there are multiple entries, pick the first one.
return (countries && countries[0]) ||
(defaultPhoneNumber && defaultPhoneNumber.getCountry()) || null;
}