When you update state in React using useState with the same value as the current state, React performs an optimization that prevents unnecessary re-renders. Here's a more detailed explanation:
React's Optimization :
- Object.is Comparison:
- React uses the
Object.is comparison algorithm to determine if the new state value is the same as the current state value.
- If
Object.is determines that the values are identical, React will typically skip re-rendering the component and its children.
- Preventing Unnecessary Re-renders:
- This optimization is crucial for performance, as it avoids unnecessary updates to the DOM.
- Re-rendering components can be computationally expensive, so skipping re-renders when the state hasn't actually changed helps to improve the efficiency of your application.
Key Points :
- Component Evaluation:
- It's important to note that even if React skips updating the DOM, it might still need to evaluate the component function itself. This is because React needs to determine whether any child components or other parts of the component's logic need to be updated.
- However, React will avoid "going deeper" into the component tree if it detects that the state hasn't changed.
- Reference Types (Objects and Arrays):
- When dealing with objects and arrays, the
Object.is comparison checks for reference equality. This means that if you create a new object or array with the same values as the previous one, React will consider them to be different, even if their contents are the same.
- Therefore, when updating objects and arrays, it is very important to make sure to create new object and array references.
- Functional Updates:
- When using functional updates, if the function returns the exact same value as the previous state, React will also bail out of the re-render.
