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

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

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

    "foo" in p;
  });

  test("conditional return", () => {
    let o = {};
    let p = new Proxy(o, {
      has(target, prop) {
        if (target.checkedFoo) return true;
        if (prop === "foo") target.checkedFoo = true;
        return false;
      },
    });

    expect("foo" in p).toBeFalse();
    expect("foo" in p).toBeTrue();
  });
});

describe("[[Has]] invariants", () => {
  test("cannot return false if the property exists and is non-configurable", () => {
    let o = {};
    Object.defineProperty(o, "foo", { configurable: false });

    p = new Proxy(o, {
      has() {
        return false;
      },
    });

    expect(() => {
      "foo" in p;
    }).toThrowWithMessage(
      TypeError,
      "Proxy handler's has trap violates invariant: a property cannot be reported as non-existent if it exists on the target as a non-configurable property"
    );
  });

  test("cannot return false if the property exists and the target is non-extensible", () => {
    let o = {};
    Object.defineProperty(o, "foo", { value: 10, configurable: true });

    let p = new Proxy(o, {
      has() {
        return false;
      },
    });

    Object.preventExtensions(o);

    expect(() => {
      "foo" in p;
    }).toThrowWithMessage(
      TypeError,
      "Proxy handler's has trap violates invariant: a property cannot be reported as non-existent if it exists on the target and the target is non-extensible"
    );
  });
});