Libraries: Move to Userland/Libraries/

Userland/Libraries/LibJS/Tests/classes/class-advanced-extends.js

@@ -0,0 +1,35 @@
+test("extending function", () => {
+    class A extends function () {
+        this.foo = 10;
+    } {}
+
+    expect(new A().foo).toBe(10);
+});
+
+test("extending null", () => {
+    class A extends null {}
+
+    expect(Object.getPrototypeOf(A.prototype)).toBeNull();
+
+    expect(() => {
+        new A();
+    }).toThrowWithMessage(ReferenceError, "|this| has not been initialized");
+});
+
+test("extending String", () => {
+    class MyString extends String {}
+
+    const ms = new MyString("abc");
+    expect(ms).toBeInstanceOf(MyString);
+    expect(ms).toBeInstanceOf(String);
+    expect(ms.charAt(1)).toBe("b");
+
+    class MyString2 extends MyString {
+        charAt(i) {
+            return `#${super.charAt(i)}`;
+        }
+    }
+
+    const ms2 = new MyString2("abc");
+    expect(ms2.charAt(1)).toBe("#b");
+});