Why is State Incorrect When Handling Events with Event Listeners in React Hooks?

Wrong React Hooks Behavior with Event Listener

Problem: When using React Hooks and handling events with event listeners, the state displayed in the console is incorrect. Specifically, clicking a button inside a card should show the updated state (number of cards), but it incorrectly displays the original state.

Code Explanation:

The problem arises due to how event listeners are registered in functional components using the useState hook. In the provided example, the handleCardClick function is defined within the CardsProvider functional component, and it always references the initial state when called.

On the other hand, handleButtonClick is defined in the Card functional component and is passed as a prop. Since it's re-registered on each render, it references the fresh state. Hence, while handleCardClick displays the wrong state, handleButtonClick displays the correct state.

Solutions:

1. Mutable State:

Instead of useState, use useRef to store a mutable state. However, this approach is not recommended for updating state, as it's an anti-pattern in both class and function components.

2. State Updater Function:

Use a state updater function inside the event listener that receives the fresh state instead of the stale state.

3. Manual Event Listener Re-registration:

Re-register the event listener every time, ensuring that it has access to the latest state.

4. Built-in Event Handling:

Use React's built-in event handling by passing the event listener directly into the DOM event handler, such as onClick={eventListener}.

Note: In the final version of React 16.8, useState only supports immutable state. Therefore, the mutable state solution described in the original answer is no longer applicable.

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