describe("normal functionality", () => { test("non-configurable property", () => { let o = {}; Object.defineProperty(o, "foo", { value: 1, writable: false, enumerable: false }); expect(o.foo).toBe(1); o.foo = 2; expect(o.foo).toBe(1); expect(o).not.toHaveConfigurableProperty("foo"); expect(o).not.toHaveEnumerableProperty("foo"); expect(o).not.toHaveWritableProperty("foo"); expect(o).toHaveValueProperty("foo", 1); }); test("array index getter", () => { let o = {}; Object.defineProperty(o, 2, { get() { return 10; }, }); expect(o[2]).toBe(10); }); test("configurable property", () => { let o = {}; Object.defineProperty(o, "foo", { value: "hi", writable: true, enumerable: true }); expect(o.foo).toBe("hi"); o.foo = "ho"; expect(o.foo).toBe("ho"); expect(o).not.toHaveConfigurableProperty("foo"); expect(o).toHaveEnumerableProperty("foo"); expect(o).toHaveWritableProperty("foo"); expect(o).toHaveValueProperty("foo", "ho"); }); test("reconfigure configurable property", () => { let o = {}; Object.defineProperty(o, "foo", { value: 9, configurable: true, writable: false }); Object.defineProperty(o, "foo", { configurable: true, writable: true }); expect(o).toHaveConfigurableProperty("foo"); expect(o).toHaveWritableProperty("foo"); expect(o).not.toHaveEnumerableProperty("foo"); expect(o).toHaveValueProperty("foo", 9); }); test("define accessor", () => { let o = {}; Object.defineProperty(o, "foo", { configurable: true, get() { return o.secret_foo + 1; }, set(value) { this.secret_foo = value + 1; }, }); o.foo = 10; expect(o.foo).toBe(12); o.foo = 20; expect(o.foo).toBe(22); Object.defineProperty(o, "foo", { configurable: true, value: 4 }); expect(o.foo).toBe(4); expect((o.foo = 5)).toBe(5); expect((o.foo = 4)).toBe(4); }); }); describe("errors", () => { test("redefine non-configurable property", () => { let o = {}; Object.defineProperty(o, "foo", { value: 1, writable: true, enumerable: true }); expect(() => { Object.defineProperty(o, "foo", { value: 2, writable: false, enumerable: true }); }).toThrowWithMessage( TypeError, "Cannot change attributes of non-configurable property 'foo'" ); }); test("cannot define 'value' and 'get' in the same descriptor", () => { let o = {}; expect(() => { Object.defineProperty(o, "a", { get() {}, value: 9, }); }).toThrowWithMessage( TypeError, "Accessor property descriptor cannot specify a value or writable key" ); }); test("cannot define 'value' and 'set' in the same descriptor", () => { let o = {}; expect(() => { Object.defineProperty(o, "a", { set() {}, writable: true, }); }).toThrowWithMessage( TypeError, "Accessor property descriptor cannot specify a value or writable key" ); }); test("redefine non-configurable accessor", () => { let o = {}; Object.defineProperty(o, "foo", { configurable: false, get() { return this.secret_foo + 2; }, set(value) { o.secret_foo = value + 2; }, }); expect(() => { Object.defineProperty(o, "foo", { configurable: false, get() { return this.secret_foo + 2; }, }); }).toThrowWithMessage( TypeError, "Cannot change attributes of non-configurable property 'foo'" ); }); });