Published at: August 20, 2022
Performance optimization is always a top concern for developers, especially as apps grow in complexity. With the introduction of React 18, performance optimizations are more important than ever. React 18 introduces exciting features like Concurrent Rendering and Automatic Batching, which can significantly boost the performance of your app. However, it’s essential to understand how to leverage these tools correctly to avoid unnecessary re-renders and optimize your app’s speed.
In this blog post, we’ll explore React.memo, useMemo, useCallback, and how React 18’s new features can be used to fine-tune performance for the best user experience.
1. React 18’s Performance Optimizations
React 18 introduces a host of new performance optimizations. One of the key features is Concurrent Rendering, which improves the responsiveness of React apps by allowing React to render updates in a non-blocking way. This means React can pause rendering to work on more important updates, keeping the UI snappy and responsive.
Automatic Batching is another feature introduced in React 18. It allows React to batch updates from multiple events (like button clicks, input changes, etc.) into a single re-render, which reduces the number of renders and improves performance. However, this doesn’t mean you don’t need to optimize individual components.
Now, let’s break down some best practices you can use to prevent unnecessary re-renders and boost performance with React.memo, useMemo, and useCallback.
2. Using React.memo for Component Memoization
In React, functional components re-render every time their parent component re-renders, which can sometimes result in unnecessary performance overhead. React.memo helps you optimize this behavior by memoizing the rendered output of a component, preventing unnecessary re-renders when the props haven’t changed.
How React.memo Works:
import React from 'react';
const MyComponent = React.memo(({ title }) => {
console.log('Rendering MyComponent');
return <h1>{title}</h1>;
});
export default MyComponent;
In the example above, React.memo wraps the MyComponent, ensuring it only re-renders when the title prop changes. If title remains the same, React will skip rendering the component and reuse the previous output.
When to Use React.memo:
- When your component has pure render logic (i.e., it renders the same output for the same input).
- When your component is part of a large list or is reused multiple times in your app.
- When your component receives complex props (objects or arrays) that don’t change often.
3. Optimizing Expensive Calculations with useMemo
React’s useMemo hook is a tool for memoizing values derived from calculations or function calls. When a component re-renders, any expensive calculations or computations will be recalculated. With useMemo, React will only recompute the result if the dependencies have changed.
How useMemo Works:
import React, { useMemo } from 'react';
const ExpensiveComponent = ({ data }) => {
const expensiveCalculation = useMemo(() => {
console.log('Running expensive calculation');
return data.reduce((acc, num) => acc + num, 0);
}, [data]);
return <div>{expensiveCalculation}</div>;
};
export default ExpensiveComponent;
In the above example, useMemo ensures that the expensive calculation (summing the numbers) is only recalculated when the data prop changes, reducing unnecessary recalculations on every render.
When to Use useMemo:
- When performing expensive calculations that don’t need to run on every render.
- When working with complex objects or arrays that don’t change frequently.
- When optimizing rendering performance for large lists or grids.
4. Using useCallback for Memoizing Functions
Similar to useMemo, useCallback is used to memoize functions to prevent unnecessary re-creation of functions on each render. This is especially useful when functions are passed down as props to child components, as it avoids triggering unnecessary re-renders.
How useCallback Works:
import React, { useState, useCallback } from 'react';
const Button = React.memo(({ onClick }) => {
console.log('Rendering Button');
return <button onClick={onClick}>Click Me</button>;
});
const ParentComponent = () => {
const [count, setCount] = useState(0);
const increment = useCallback(() => setCount(count + 1), [count]);
return (
<div>
<h1>{count}</h1>
<Button onClick={increment} />
</div>
);
};
export default ParentComponent;
In the example above, useCallback is used to memoize the increment function, so it only changes when count changes. The Button component only re-renders when the onClick prop changes, which avoids unnecessary renders.
When to Use useCallback:
- When passing functions as props to child components.
- When a child component relies on the function reference (e.g., for
React.memooptimization). - When using functions inside hooks that depend on props or state values.
5. React 18’s Concurrent Rendering and Automatic Batching
React 18 introduces Concurrent Rendering, which is designed to improve the overall performance of React apps by allowing React to pause and resume rendering as needed. This enables the rendering process to be non-blocking, ensuring the UI stays responsive even during heavy updates.
Concurrent Rendering also works in tandem with Automatic Batching, which batches multiple state updates (e.g., from different events) into a single re-render. This reduces the number of renders and improves performance.
To take advantage of this new feature, you don’t have to change anything in your existing code. However, using startTransition() for non-urgent updates (like fetching data) allows React to prioritize higher-priority updates (e.g., input changes) and defer non-urgent ones.
Example with startTransition():
import React, { useState, useTransition } from 'react';
const ExpensiveList = ({ data }) => {
return <div>{data.map(item => <div key={item}>{item}</div>)}</div>;
};
const ParentComponent = () => {
const [isPending, startTransition] = useTransition();
const [filter, setFilter] = useState('');
const handleFilterChange = (event) => {
const value = event.target.value;
startTransition(() => {
setFilter(value);
});
};
return (
<div>
<input type="text" value={filter} onChange={handleFilterChange} />
{isPending ? <span>Loading...</span> : <ExpensiveList data={filterData(data, filter)} />}
</div>
);
};
export default ParentComponent;
In this example, startTransition allows the filtering of the list to be deferred while keeping the input field responsive. The expensive list rendering happens in the background, and the UI stays fluid.
6. Conclusion
React 18 brings several performance improvements, but it’s important to use them wisely to get the most out of your app. By leveraging React.memo, useMemo, useCallback, and Concurrent Rendering, you can avoid unnecessary re-renders, reduce CPU usage, and improve overall UI responsiveness.
These tools allow you to optimize expensive calculations, prevent redundant renders, and fine-tune your React app’s performance to meet the needs of modern applications.
To stay ahead, take full advantage of React 18’s new features and best practices to create faster, more responsive React apps that provide an excellent user experience.
