In the application (sales dashboard in React+Redux), users report that it does not work as expected. Find the problems and fix them. The application contains: a product list sorted by sales, sales visualization in a bar chart (ECharts), a form for adding new products. Main complaint: the product is supposedly added through the form but does not appear in the list.

The main reason why a new product does not appear in the list after being added through the form is usually related to the Redux state not updating correctly or the list component not re-rendering.

Checks and fixes:

1. Check action and reducer:

   • Ensure that the correct action with the new product is dispatched when submitting the form.
   • In the reducer, adding a new product should return a new array with the added item, not mutate the existing one.

2. Immutability of state:

   • If you mutate the array in the reducer (e.g., push), React-Redux may not detect the change.
   • Use methods that return a new array, for example: return [...state, newProduct].

3. Component subscription:

   • Check that the product list component is subscribed to the correct slice of the Redux state.
   • If using connect or useSelector, ensure the selector returns the updated array.

4. Updating visualization (ECharts):

   • After updating the product list, update the chart data.
   • Make sure the chart data is taken from the current state.

5. Example of a fixed reducer:

function productsReducer(state = [], action) {
  switch (action.type) {
    case 'ADD_PRODUCT':
      return [...state, action.payload]; // create a new array
    default:
      return state;
  }
}

6. Example of dispatch from the form:

const dispatch = useDispatch();

const onSubmit = (product) => {
  dispatch({ type: 'ADD_PRODUCT', payload: product });
};

7. Checking the list component:

const products = useSelector(state => state.products);

return (
  <ul>
    {products.map(p => <li key={p.id}>{p.name} - {p.sales}</li>)}
  </ul>
);

If these points are considered, the new product will be added and displayed correctly.