`memo()` vs. `useMemo()` in React: A Comparison
Both `memo()` and `useMemo()` are optimization techniques in React that help prevent unnecessary re-renders, but they serve slightly different purposes:
`React.memo()`
* Purpose: Prevents unnecessary re-renders of functional components based on prop changes.
* How it works: Memoizes the component's result and only re-renders it if its props have changed.
* Use case: Optimizing components that are expensive to render and don't need to re-render unless their props change.
Example:
```javascript
import React, { memo } from 'react';
const MyComponent = memo(({ name }) => {
console.log('MyComponent rendered');
return <div>{name}</div>;
});
```
`useMemo()`
* Purpose: Memoizes the result of an expensive function call within a component.
* How it works: Caches the result of the function and only re-calculates it if its dependencies have changed.
* Use case: Optimizing computationally expensive calculations within components.
Example:
```javascript
import React, { useMemo } from 'react';
const MyComponent = ({ data }) => {
const expensiveCalculation = useMemo(() => {
console.log('Expensive calculation performed');
return data.reduce((acc, item) => acc + item.value, 0);
}, [data]);
return <div>{expensiveCalculation}</div>;
};
```
Key Differences:
- Target:`memo()` optimizes component re-renders, while `useMemo()` optimizes function calls.
- Dependencies:`memo()` uses prop equality for re-render checks, while `useMemo()` uses a dependency array for recalculation.
- Usage: `memo()` is typically used to wrap components, while `useMemo()` is used within components to memoize functions.
Choosing the Right Tool:
- Use `memo()` when you want to prevent a component from re-rendering unless its props change.
- Use `useMemo()` when you have expensive calculations within a component that you want to avoid re-computing unnecessarily.
- Remember to carefully consider the dependencies passed to both `memo()` and `useMemo()` to ensure they are optimized correctly.