ladybird/Libraries/LibJS/Tests/builtins/Proxy/Proxy.handler-deleteProperty.js

describe("[[Delete]] trap normal behavior", () => {
  test("forwarding when not defined in handler", () => {
    expect(delete new Proxy({}, { deleteProperty: undefined }).foo).toBeTrue();
    expect(delete new Proxy({}, { deleteProperty: null }).foo).toBeTrue();
    expect(delete new Proxy({}, {}).foo).toBeTrue();
  });

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

    delete p.foo;
  });

  test("conditional deletion", () => {
    o = { foo: 1, bar: 2 };
    p = new Proxy(o, {
      deleteProperty(target, property) {
        if (property === "foo") {
          delete target[property];
          return true;
        }
        return false;
      },
    });

    expect(delete p.foo).toBeTrue();
    expect(delete p.bar).toBeFalse();

    expect(o.foo).toBeUndefined();
    expect(o.bar).toBe(2);
  });
});

describe("[[Delete]] invariants", () => {
  test("cannot report a non-configurable own property as deleted", () => {
    let o = {};
    Object.defineProperty(o, "foo", { configurable: false });
    let p = new Proxy(o, {
      deleteProperty() {
        return true;
      },
    });

    expect(() => {
      delete p.foo;
    }).toThrowWithMessage(
      TypeError,
      "Proxy handler's deleteProperty trap violates invariant: cannot report a non-configurable own property of the target as deleted"
    );
  });
});