LibJS: Implement Intl.DateTimeFormat.supportedLocalesOf

Author: https://github.com/trflynn89
Commit: https://github.com/SerenityOS/serenity/commit/d0e1997e07f
Pull-request: https://github.com/SerenityOS/serenity/pull/11128
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Runtime/Intl/DateTimeFormatConstructor.cpp

@@ -5,7 +5,9 @@
  */
 
 #include <LibJS/Runtime/AbstractOperations.h>
+#include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/Intl/AbstractOperations.h>
 #include <LibJS/Runtime/Intl/DateTimeFormat.h>
 #include <LibJS/Runtime/Intl/DateTimeFormatConstructor.h>
 
@@ -25,6 +27,10 @@ void DateTimeFormatConstructor::initialize(GlobalObject& global_object)
 
     // 11.3.1 Intl.DateTimeFormat.prototype, https://tc39.es/ecma402/#sec-intl.datetimeformat.prototype
     define_direct_property(vm.names.prototype, global_object.intl_date_time_format_prototype(), 0);
+
+    u8 attr = Attribute::Writable | Attribute::Configurable;
+    define_native_function(vm.names.supportedLocalesOf, supported_locales_of, 1, attr);
+
     define_direct_property(vm.names.length, Value(0), Attribute::Configurable);
 }
 
@@ -58,4 +64,19 @@ ThrowCompletionOr<Object*> DateTimeFormatConstructor::construct(FunctionObject&
     return date_time_format;
 }
 
+// 11.3.2 Intl.DateTimeFormat.supportedLocalesOf ( locales [ , options ] ), https://tc39.es/ecma402/#sec-intl.datetimeformat.supportedlocalesof
+JS_DEFINE_NATIVE_FUNCTION(DateTimeFormatConstructor::supported_locales_of)
+{
+    auto locales = vm.argument(0);
+    auto options = vm.argument(1);
+
+    // 1. Let availableLocales be %DateTimeFormat%.[[AvailableLocales]].
+
+    // 2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
+    auto requested_locales = TRY(canonicalize_locale_list(global_object, locales));
+
+    // 3. Return ? SupportedLocales(availableLocales, requestedLocales, options).
+    return TRY(supported_locales(global_object, requested_locales, options));
+}
+
 }