LibJS: Implement Proxy.revocable()

Author: https://github.com/linusg
Commit: 9b35231453
Pull-request: https://github.com/SerenityOS/serenity/pull/7926

Userland/Libraries/LibJS/Tests/builtins/Proxy/Proxy.revocable.js

@@ -0,0 +1,72 @@
+test("length is 2", () => {
+    expect(Proxy.revocable).toHaveLength(2);
+});
+
+describe("errors", () => {
+    test("constructor argument count", () => {
+        expect(() => {
+            Proxy.revocable();
+        }).toThrowWithMessage(
+            TypeError,
+            "Expected target argument of Proxy constructor to be object, got undefined"
+        );
+
+        expect(() => {
+            Proxy.revocable({});
+        }).toThrowWithMessage(
+            TypeError,
+            "Expected handler argument of Proxy constructor to be object, got undefined"
+        );
+    });
+
+    test("constructor requires objects", () => {
+        expect(() => {
+            Proxy.revocable(1, {});
+        }).toThrowWithMessage(
+            TypeError,
+            "Expected target argument of Proxy constructor to be object, got 1"
+        );
+
+        expect(() => {
+            Proxy.revocable({}, 1);
+        }).toThrowWithMessage(
+            TypeError,
+            "Expected handler argument of Proxy constructor to be object, got 1"
+        );
+    });
+});
+
+describe("normal behavior", () => {
+    test("returns object with 'proxy' and 'revoke' properties", () => {
+        const revocable = Proxy.revocable(
+            {},
+            {
+                get() {
+                    return 42;
+                },
+            }
+        );
+        expect(typeof revocable).toBe("object");
+        expect(Object.getPrototypeOf(revocable)).toBe(Object.prototype);
+        expect(revocable.hasOwnProperty("proxy")).toBeTrue();
+        expect(revocable.hasOwnProperty("revoke")).toBeTrue();
+        expect(typeof revocable.revoke).toBe("function");
+        // Can't `instanceof Proxy`, but this should do the trick :^)
+        expect(revocable.proxy.foo).toBe(42);
+    });
+
+    test("'revoke' function revokes Proxy", () => {
+        const revocable = Proxy.revocable({}, {});
+        expect(revocable.proxy.foo).toBeUndefined();
+        expect(revocable.revoke()).toBeUndefined();
+        expect(() => {
+            revocable.proxy.foo;
+        }).toThrowWithMessage(TypeError, "An operation was performed on a revoked Proxy object");
+    });
+
+    test("'revoke' called multiple times is a noop", () => {
+        const revocable = Proxy.revocable({}, {});
+        expect(revocable.revoke()).toBeUndefined();
+        expect(revocable.revoke()).toBeUndefined();
+    });
+});