Does React Guarantee Order in State Updates?

Does React Maintain Update Order for State Updates?

React's optimization for performance involves asynchronous and batched state updates. While the state may not be updated promptly after calling setState, it's essential to determine whether React maintains the order of updates within and across components.

For Updates Within a Component
Within the same component, React rigorously maintains the order of setState calls. This means that if you have multiple updates in succession, React will apply them sequentially. Thus, the final state will reflect the most recent update to each key.

For Updates Across Components
React also respects update order across different components. If you trigger state updates in different components consecutively, React will ensure that the updates are applied in the same order as the calls to setState.

Intermediate State Visibility
Whether you observe intermediate states during the update process is influenced by React's batching. By default, updates within React event handlers are batched. Consequently, you will not see intermediate states for updates initiated within event handlers.

React 17 and Prior
Prior to React 17, updates outside of event handlers were not batched by default. In such cases, you could encounter intermediate states. However, React provided an unstable API, ReactDOM.unstable_batchedUpdates(), to force batching in these instances.

React 18 and Later
Starting with React 18, all updates are batched by default. This means that updates outside of event handlers will also be batched, effectively eliminating intermediate state visibility for most scenarios. If necessary, you can use flushSync to override batching for specific updates.

Conclusion
React upholds the order of state updates, regardless of whether they occur within the same component or across different components. The batching behavior determines whether you will observe intermediate states during the update process. React 18's default batching reduces intermediate state visibility, promoting a smoother user experience.

The above is the detailed content of Does React Guarantee Order in State Updates?. For more information, please follow other related articles on the PHP Chinese website!