LibJS: Implement Intl.NumberFormat.supportedLocalesOf

Author: https://github.com/trflynn89
Commit: https://github.com/SerenityOS/serenity/commit/071e193d92a
Pull-request: https://github.com/SerenityOS/serenity/pull/9945
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Runtime/Intl/NumberFormatConstructor.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/NumberFormat.h>
@@ -390,6 +391,10 @@ void NumberFormatConstructor::initialize(GlobalObject& global_object)
 
     // 15.3.1 Intl.NumberFormat.prototype, https://tc39.es/ecma402/#sec-intl.numberformat.prototype
     define_direct_property(vm.names.prototype, global_object.intl_number_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);
 }
 
@@ -427,4 +432,21 @@ Value NumberFormatConstructor::construct(FunctionObject& new_target)
     return number_format;
 }
 
+// 15.3.2 Intl.NumberFormat.supportedLocalesOf ( locales [ , options ] ), https://tc39.es/ecma402/#sec-intl.numberformat.supportedlocalesof
+JS_DEFINE_NATIVE_FUNCTION(NumberFormatConstructor::supported_locales_of)
+{
+    auto locales = vm.argument(0);
+    auto options = vm.argument(1);
+
+    // 1. Let availableLocales be %NumberFormat%.[[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/NumberFormatConstructor.h

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

Userland/Libraries/LibJS/Tests/builtins/Intl/NumberFormat/NumberFormat.supportedLocalesOf.js

@@ -0,0 +1,43 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Intl.NumberFormat.supportedLocalesOf).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        // prettier-ignore
+        const values = [
+            [[], []],
+            [undefined, []],
+            ["en", ["en"]],
+            [new Intl.Locale("en"), ["en"]],
+            [["en"], ["en"]],
+            [["en", "en-gb", "en-us"], ["en", "en-GB", "en-US"]],
+            [["en", "de", "fr"], ["en", "de", "fr"]],
+            [["en-foobar"], ["en-foobar"]],
+            [["en-foobar-u-abc"], ["en-foobar-u-abc"]],
+            [["aa", "zz"], []],
+            [["en", "aa", "zz"], ["en"]],
+        ];
+        for (const [input, expected] of values) {
+            expect(Intl.NumberFormat.supportedLocalesOf(input)).toEqual(expected);
+            // "best fit" (implementation defined) just uses the same implementation as "lookup" at the moment
+            expect(
+                Intl.NumberFormat.supportedLocalesOf(input, { localeMatcher: "best fit" })
+            ).toEqual(Intl.NumberFormat.supportedLocalesOf(input, { localeMatcher: "lookup" }));
+        }
+    });
+});
+
+describe("errors", () => {
+    test("invalid value for localeMatcher option", () => {
+        expect(() => {
+            Intl.NumberFormat.supportedLocalesOf([], { localeMatcher: "foo" });
+        }).toThrowWithMessage(RangeError, "foo is not a valid value for option localeMatcher");
+    });
+
+    test("invalid language tag", () => {
+        expect(() => {
+            Intl.NumberFormat.supportedLocalesOf(["aaaaaaaaa"]);
+        }).toThrowWithMessage(RangeError, "aaaaaaaaa is not a structurally valid language tag");
+    });
+});