[FIX] reactivity: work even if no callback is given

src/reactivity.ts

@@ -130,7 +130,7 @@ const reactiveCache = new WeakMap<Target, WeakMap<Callback, Reactive>>();
  *  reactive has changed
  * @returns a proxy that tracks changes to it
  */
-export function reactive<T extends Target>(target: T, callback: Callback): Reactive<T> {
+export function reactive<T extends Target>(target: T, callback: Callback = () => {}): Reactive<T> {
   if (!canBeMadeReactive(target)) {
     throw new Error(`Cannot make the given value reactive`);
   }

tests/reactivity.test.ts

@@ -60,6 +60,13 @@ describe("Reactivity", () => {
     expect(Array.isArray(state)).toBe(true);
   });
 
+  test("work if there are no callback given", () => {
+    const state = reactive({ a: 1 });
+    expect(state.a).toBe(1);
+    state.a = 2;
+    expect(state.a).toBe(2);
+  });
+
   test("Throw error if value is not proxifiable", () => {
     expect(() => createReactive(1)).toThrow("Cannot make the given value reactive");
   });