Why Do React Hooks Exhibit Inconsistent State Behavior with Event Listeners?

Wrong React Hooks Behaviour with Event Listener

Overview

This article delves into an issue encountered when using React Hooks, specifically concerning the inconsistent behavior of state console logging when triggered by event listeners within custom components.

Problem Statement

Consider the given CodeSandbox: https://codesandbox.io/s/lrxw1wr97m. Following these steps:

1. Click the "Add card" button twice to create two cards.
2. In the first card, click "Button1" to display the correct number of cards (2) in the console.
3. In the first card, click "Button2" (which is handled by an event listener) to observe an incorrect display of only one card in the console.

The issue arises when attempting to display the updated state from within the event listener attached to "Button2".

Root Cause

The discrepancy in state display stems from the different ways event handlers are implemented in the CardsProvider and Card components.

• CardsProvider: Event handlers are defined within the functional component's scope, creating new functions with references to the current state at definition time.
• Card: Event handlers are received as props and registered once on component mount. However, these handlers reference a stale state that may not represent the current state.

Solutions

Several approaches can resolve this issue:

Mutable State:

Mutable state values such as those provided by useRef can be employed to retain the latest state changes. However, this method is not recommended as useState is meant for managing immutable state.

State Updater Function:

Using state updater functions allows for passing the latest state to the callback, ensuring that the state displayed is always current.

Manual Event Listener Re-registration:

Alternatively, event listeners can be re-registered with each state update to guarantee access to the current state.

Built-in Event Handling:

When possible, utilizing React's native DOM event handling mechanism eliminates the need for manual event listener management.

Summary

The inconsistency in state display with event listener handling can be attributed to the differing treatment of event handlers within the affected components. By adopting appropriate solutions, developers can alleviate this issue and maintain correct state behavior.

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