ReactJS
Understanding React.memo: Optimize React Performance
Introduction
Memo is a higher-order component in React that optimizes functional components. It prevents them from rerendering unnecessarily, making use of memoizing the output of the component such that it is only rerendered if props change.
When you wrap a component with React.memo, React compares the previous props with the next props. If the props are shallowly equal (i.e., their values haven't changed) React will skip rerendering the component and reuse the last rendered output.
Examples
Here's a basic example of using React.memo:
import React from 'react';const MyComponent = React.memo(function MyComponent(props) { console.log('Rendered!'); return <div>{props.value}</div>;});// Usage<MyComponent value="Hello" />
In this example, MyComponent will only rerender if the value prop changes.
When to Use React.memo
- Pure Components: The component is "pure" if the rendering of that component depends on its props only. If props do not change, the output will be the same, it's a good candidate for memoization.
- Expensive Renders: If the component has an expensive rendering process, like complex calculations or heavy DOM manipulations, memoizing it will save quite a lot of rendering time.
- Frequent Re-renders: When the parent component re-renders frequently, but the child component's props remain the same most of the time, React.memo can prevent unnecessary re-renders of the child component.
When Not to Use React.memo
- Low-cost Components: If the component is lightweight and re-renders quickly, using React.memo might introduce unnecessary complexity without significant performance benefits.
- State or Context-Dependent: If the component relies on internal state or context that frequently changes, React.memo may not provide much benefit.
- Props are Functions or Objects: Since React.memo does a shallow comparison, if you pass functions or objects as props that change on every render (e.g., inline functions or object literals), the component will still re-render unless these props are memoized with useCallback or useMemo.
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