The second parameter scheduler of effect

Description of Functionality

1. A function is passed as the second parameter of the effect, and it is commonly referred to as the scheduler.

2. The first parameter fn of the effect will be called upon initialization (first execution).

3. When the reactive object updates (set), the function fn will not be executed directly; instead, the scheduler will be invoked.

4. When the runner function is called, it will execute the function fn again.