LibJS: Implement Intl.ListFormat.supportedLocalesOf

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

@@ -5,6 +5,7 @@
  */
 
 #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/ListFormat.h>
@@ -27,6 +28,10 @@ void ListFormatConstructor::initialize(GlobalObject& global_object)
 
     // 13.3.1 Intl.ListFormat.prototype, https://tc39.es/ecma402/#sec-Intl.ListFormat.prototype
     define_direct_property(vm.names.prototype, global_object.intl_list_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);
 }
 
@@ -103,4 +108,21 @@ Value ListFormatConstructor::construct(FunctionObject& new_target)
     return list_format;
 }
 
+// 13.3.2 Intl.ListFormat.supportedLocalesOf ( locales [ , options ] ), https://tc39.es/ecma402/#sec-Intl.ListFormat.supportedLocalesOf
+JS_DEFINE_NATIVE_FUNCTION(ListFormatConstructor::supported_locales_of)
+{
+    auto locales = vm.argument(0);
+    auto options = vm.argument(1);
+
+    // 1. Let availableLocales be %DisplayNames%.[[AvailableLocales]].
+
+    // 2. Let requestedLocales be ? CanonicalizeLocaleList(locales).
+    auto requested_locales = canonicalize_locale_list(global_object, locales);
+    if (vm.exception())
+        return {};
+
+    // 3. Return ? SupportedLocales(availableLocales, requestedLocales, options).
+    return supported_locales(global_object, requested_locales, options);
+}
+
 }

Userland/Libraries/LibJS/Runtime/Intl/ListFormatConstructor.h

@@ -23,6 +23,8 @@ public:
 
 private:
     virtual bool has_constructor() const override { return true; }
+
+    JS_DECLARE_NATIVE_FUNCTION(supported_locales_of);
 };
 
 }