serenity/Userland/Libraries/LibJS/Tests/builtins/Proxy/Proxy.handler-getOwnPropertyDescriptor.js

describe("[Call][GetOwnProperty]] trap normal behavior", () => {
    test("forwarding when not defined in handler", () => {
        expect(
            Object.getOwnPropertyDescriptor(new Proxy({}, { getOwnPropertyDescriptor: null }), "a")
        ).toBeUndefined();
        expect(
            Object.getOwnPropertyDescriptor(
                new Proxy({}, { getOwnPropertyDescriptor: undefined }),
                "a"
            )
        ).toBeUndefined();
        expect(Object.getOwnPropertyDescriptor(new Proxy({}, {}), "a")).toBeUndefined();
    });

    test("correct arguments supplied to trap", () => {
        let o = {};
        let p = new Proxy(o, {
            getOwnPropertyDescriptor(target, property) {
                expect(target).toBe(o);
                expect(property).toBe("foo");
            },
        });

        Object.getOwnPropertyDescriptor(p, "foo");
    });

    test("conditional returned descriptor", () => {
        let o = { foo: "bar" };
        Object.defineProperty(o, "baz", {
            value: "qux",
            enumerable: false,
            configurable: true,
            writable: false,
        });

        let p = new Proxy(o, {
            getOwnPropertyDescriptor(target, property) {
                if (property === "baz") return Object.getOwnPropertyDescriptor(target, "baz");
                return {
                    value: target[property],
                    enumerable: false,
                    configurable: true,
                    writable: true,
                };
            },
        });

        expect(p).toHaveConfigurableProperty("baz");
        expect(p).not.toHaveEnumerableProperty("baz");
        expect(p).not.toHaveWritableProperty("baz");
        expect(p).toHaveValueProperty("baz", "qux");
        expect(p).not.toHaveGetterProperty("baz");
        expect(p).not.toHaveSetterProperty("baz");

        d = Object.getOwnPropertyDescriptor(p, "foo");

        expect(p).toHaveConfigurableProperty("foo");
        expect(p).not.toHaveEnumerableProperty("foo");
        expect(p).toHaveWritableProperty("foo");
        expect(p).toHaveValueProperty("foo", "bar");
        expect(p).not.toHaveGetterProperty("foo");
        expect(p).not.toHaveSetterProperty("foo");
    });
});

describe("[[GetOwnProperty]] invariants", () => {
    test("must return an object or undefined", () => {
        expect(() => {
            Object.getOwnPropertyDescriptor(
                new Proxy(
                    {},
                    {
                        getOwnPropertyDescriptor() {
                            return 1;
                        },
                    }
                )
            );
        }).toThrowWithMessage(
            TypeError,
            "Proxy handler's getOwnPropertyDescriptor trap violates invariant: must return an object or undefined"
        );
    });

    test("cannot return undefined for a non-configurable property", () => {
        let o = {};
        Object.defineProperty(o, "foo", { value: 10, configurable: false });

        let p = new Proxy(o, {
            getOwnPropertyDescriptor() {
                return undefined;
            },
        });

        expect(Object.getOwnPropertyDescriptor(p, "bar")).toBeUndefined();

        expect(() => {
            Object.getOwnPropertyDescriptor(p, "foo");
        }).toThrowWithMessage(
            TypeError,
            "Proxy handler's getOwnPropertyDescriptor trap violates invariant: cannot return undefined for a property on the target which is a non-configurable property"
        );
    });

    test("cannot return undefined for an existing property if the target is non-extensible", () => {
        let o = {};
        Object.defineProperty(o, "baz", {
            value: 20,
            configurable: true,
            writable: true,
            enumerable: true,
        });
        Object.preventExtensions(o);

        let p = new Proxy(o, {
            getOwnPropertyDescriptor() {
                return undefined;
            },
        });

        expect(() => {
            Object.getOwnPropertyDescriptor(p, "baz");
        }).toThrowWithMessage(
            TypeError,
            "Proxy handler's getOwnPropertyDescriptor trap violates invariant: cannot report a property as being undefined if it exists as an own property of the target and the target is non-extensible"
        );
    });

    test("invalid property descriptors", () => {
        let o = {};
        Object.defineProperty(o, "v1", { value: 10, configurable: false });
        Object.defineProperty(o, "v2", { value: 10, configurable: false, enumerable: true });
        Object.defineProperty(o, "v3", {
            configurable: false,
            get() {
                return 1;
            },
        });
        Object.defineProperty(o, "v4", {
            value: 10,
            configurable: false,
            writable: false,
            enumerable: true,
        });

        expect(() => {
            Object.getOwnPropertyDescriptor(
                new Proxy(o, {
                    getOwnPropertyDescriptor() {
                        return { configurable: true };
                    },
                }),
                "v1"
            );
        }).toThrowWithMessage(
            TypeError,
            "Proxy handler's getOwnPropertyDescriptor trap violates invariant: invalid property descriptor for existing property on the target"
        );

        expect(() => {
            Object.getOwnPropertyDescriptor(
                new Proxy(o, {
                    getOwnPropertyDescriptor() {
                        return { enumerable: false };
                    },
                }),
                "v2"
            );
        }).toThrowWithMessage(
            TypeError,
            "Proxy handler's getOwnPropertyDescriptor trap violates invariant: invalid property descriptor for existing property on the target"
        );

        expect(() => {
            Object.getOwnPropertyDescriptor(
                new Proxy(o, {
                    getOwnPropertyDescriptor() {
                        return { value: 10 };
                    },
                }),
                "v3"
            );
        }).toThrowWithMessage(
            TypeError,
            "Proxy handler's getOwnPropertyDescriptor trap violates invariant: invalid property descriptor for existing property on the target"
        );

        expect(() => {
            Object.getOwnPropertyDescriptor(
                new Proxy(o, {
                    getOwnPropertyDescriptor() {
                        return { value: 10, writable: true };
                    },
                }),
                "v4"
            );
        }).toThrowWithMessage(
            TypeError,
            "Proxy handler's getOwnPropertyDescriptor trap violates invariant: invalid property descriptor for existing property on the target"
        );
    });

    test("cannot report a property as non-configurable if it does not exist or is non-configurable", () => {
        let o = {};
        Object.defineProperty(o, "v", { configurable: true });
        expect(() => {
            Object.getOwnPropertyDescriptor(
                new Proxy(o, {
                    getOwnPropertyDescriptor() {
                        return { configurable: false };
                    },
                }),
                "v"
            );
        }).toThrowWithMessage(
            TypeError,
            "Proxy handler's getOwnPropertyDescriptor trap violates invariant: cannot report target's property as non-configurable if the property does not exist, or if it is configurable"
        );
    });
});