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_js-findClosestLocale - Gets the closest locale from the available locales
// rev3 -
* Selects the closest matching locale from a list of locales.
* @param aLocales
* An array of available locales
* @param aMatchLocales
* An array of prefered locales, ordered by priority. Most wanted first.
* Locales have to be in lowercase.
* @return the best match for the currently selected locale
* Stolen from
function findClosestLocale(aLocales, aMatchLocales) {
aMatchLocales = aMatchLocales;
// Holds the best matching localized resource
let bestmatch = null;
// The number of locale parts it matched with
let bestmatchcount = 0;
// The number of locale parts in the match
let bestpartcount = 0;
for (let locale of aMatchLocales) {
let lparts = locale.split("-");
for (let localized of aLocales) {
let found = localized.toLowerCase();
// Exact match is returned immediately
if (locale == found)
return localized;
let fparts = found.split("-");
/* If we have found a possible match and this one isn't any longer
then we dont need to check further. */
if (bestmatch && fparts.length < bestmatchcount)
// Count the number of parts that match
let maxmatchcount = Math.min(fparts.length, lparts.length);
let matchcount = 0;
while (matchcount < maxmatchcount &&
fparts[matchcount] == lparts[matchcount])
/* If we matched more than the last best match or matched the same and
this locale is less specific than the last best match. */
if (matchcount > bestmatchcount ||
(matchcount == bestmatchcount && fparts.length < bestpartcount)) {
bestmatch = localized;
bestmatchcount = matchcount;
bestpartcount = fparts.length;
// If we found a valid match for this locale return it
if (bestmatch)
return bestmatch;
return null;

Noitidart commented Nov 23, 2016




  • Added rev and link comment


  • Removed fall back to getPreferredLocales() as that isn't available
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