LibJS: Implement Intl.Locale.prototype.baseName

Author: https://github.com/trflynn89
Commit: 21b3c5edba
Pull-request: https://github.com/SerenityOS/serenity/pull/9749
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Tests/builtins/Intl/Locale/Locale.prototype.baseName.js

@@ -0,0 +1,21 @@
+describe("errors", () => {
+    test("called on non-Locale object", () => {
+        expect(() => {
+            Intl.Locale.prototype.baseName;
+        }).toThrowWithMessage(TypeError, "Not a Intl.Locale object");
+    });
+});
+
+describe("normal behavior", () => {
+    test("basic functionality", () => {
+        expect(new Intl.Locale("en").baseName).toBe("en");
+        expect(new Intl.Locale("en-Latn").baseName).toBe("en-Latn");
+        expect(new Intl.Locale("en-GB").baseName).toBe("en-GB");
+        expect(new Intl.Locale("en", { script: "Latn" }).baseName).toBe("en-Latn");
+        expect(new Intl.Locale("en", { region: "GB" }).baseName).toBe("en-GB");
+
+        expect(new Intl.Locale("en-u-ca-abc").baseName).toBe("en");
+        expect(new Intl.Locale("en", { calendar: "abc" }).baseName).toBe("en");
+        expect(new Intl.Locale("en-x-abcd").baseName).toBe("en");
+    });
+});