How to be Better with Performance Optimization in React

Why is Performance Important in React?

React has quickly become one of the most popular JavaScript frameworks for building complex, interactive user interfaces. However, with great power comes great responsibility, and React’s flexibility and strength can come at a cost – performance.

In the web development world, performance is critical. Slow page load times and unresponsive user interfaces can lead to frustrated users and lost revenue. This is particularly true in the modern web, where users expect fast and responsive applications that work across a variety of devices and network conditions.

React’s virtual DOM helps to optimize rendering speed, but there are still a number of factors that can affect the performance of a React application. For example, large components with many nested child components can result in slow rendering times, leading to laggy and unresponsive interfaces.

What makes Reactjs performance faster?

There are a number of techniques that can be used to improve the performance of React applications. One such technique is to use shallow comparison to determine if a component needs to be re-rendered. When a component’s props or state change, React re-renders the component. However, if the props and state have not changed, there is no need to re-render the component. The shallow comparison allows React to quickly determine if the props and state have changed, reducing unnecessary re-renders and improving performance.

Another technique for improving React performance is using the shouldComponentUpdate() method. This method allows developers to control when a component should re-render by returning a boolean value. By implementing shouldComponentUpdate() method, developers can prevent unnecessary re-renders and improve performance.

React also provides two built-in optimizations for improving performance – React.PureComponent and React.memo(). React.PureComponent is a base class for components that implements shouldComponentUpdate() with a shallow comparison of props and state. React.memo() is a higher-order component that memoizes (caching the results from before) the result of a component’s render method based on its props. These built-in optimizations can significantly reduce the number of re-renders, improving the performance of React applications.

In addition to these techniques, there are a number of other techniques for improving the performance of React applications. For example, Server-side rendering can improve initial page load times and SEO. Lazy loading and code splitting can improve the performance of large applications by only loading the code that is necessary for a given page or component. Web Workers can be used to offload computationally expensive tasks to a separate thread, improving the responsiveness of the user interface. We will discuss these techniques further later in this article.

What Are the Common Performance Issues in React?

React is a powerful and flexible JavaScript library that makes it easy to build dynamic and interactive user interfaces. However, as with any software, there are potential performance issues that can arise when building with React.

• Unnecessary Re-renders: One of the most common performance issues in React is unnecessary re-renders. React is designed to re-render components whenever their props or state change. However, if a component is re-rendered when it doesn’t need to be, it can result in unnecessary work for the browser and cause the application to slow down.

To prevent unnecessary re-renders, developers can use shouldComponentUpdate() or PureComponent to limit re-renders to only when the component’s props or state have changed.

• Large Component Trees: Another performance issue in React is large component trees. When components are nested deeply, it can result in a slower rendering process as the browser must traverse the entire tree to render the page, especially for mobile users with slower internet speeds.

To prevent large component trees, developers can use lazy loading or code splitting to only load components that are needed for a given page or feature.

• Inefficient Event Handling: Event handling in React can also cause performance issues if not implemented efficiently. For example, if an event handler function is created inside a component’s render method, it will be recreated every time the component is rendered. This can result in unnecessary work for the browser and cause the application to slow down.

To prevent inefficient event handling, developers can create event handler functions outside of the render method and bind them to the component’s instance in the constructor.

Implementing shouldComponentUpdate for preventing unnecessary renders

shouldComponentUpdate() What is it? and how to implement

Shallow comparison is a technique used in React to optimize the rendering of components. By using shallow comparison, the component will only re-render when the props and state have changed, reducing the number of unnecessary re-renders and improving the performance of the component.

Shallow comparison is performed by comparing the references of the previous and next props and state. If the references are the same, it means that the props and state have not changed, and a re-render is not needed. If the references are different, it means that the props and state have changed, and a re-render is required.

This method is called before a component is re-rendered and allows developers to control whether the component should be re-rendered. By returning false from shouldComponentUpdate(), we can prevent a component from re-rendering when the props and state have not changed.

import React from 'react';

class MyComponent extends React.Component {
  shouldComponentUpdate(nextProps, nextState) {
    return nextProps.someProp !== this.props.someProp ||
           nextState.someState !== this.state.someState;
  }

  render() {
    return <div>{this.props.someProp}</div>;
  }
}

In this example, we implement the shouldComponentUpdate() method to compare the previous and next props. If the someProp prop has changed, the component will re-render. If the someProp prop has not changed, the component will not re-render, improving the performance of the component.

In addition to shouldComponentUpdate(), React provides a PureComponent component class that implements the shouldComponentUpdate() method with a shallow comparison of props and state. By using PureComponent, we can reduce the number of re-renders and optimize the performance of the component.

import React from 'react';

class MyComponent extends React.PureComponent {
  render() {
    return <div>{this.props.someProp}</div>;
  }
}

In this example, we extend the PureComponent class and implement the render method. The PureComponent class will automatically perform a shallow comparison of the previous and next props and state, and re-render the component only when necessary.

Limitations of React.PureComponent

React.PureComponent is a class provided by React that is designed to optimize the rendering of components by reducing unnecessary re-renders. It does this by implementing the shouldComponentUpdate() method with a shallow comparison of the component’s props and state.

While React.PureComponent can be an effective way to optimize the performance of a component, it has some limitations that should be considered when using it.

• Deep Comparison of Props and State: React.PureComponent performs a shallow comparison of the component’s props and state to determine whether a re-render is necessary. This means that it only compares the references of the props and state objects, not their contents. If the props or state contain complex objects or arrays, React.PureComponent will not detect changes to their contents, resulting in unnecessary re-renders.

import React from 'react';

class MyComponent extends React.PureComponent {
  render() {
    return <div>{this.props.someProp}</div>;
  }
}

const App = () => {
  const someData = { id: 1, name: 'John' };
  
  return <MyComponent someProp={someData} />;
}

In this example, we pass an object as a prop to the MyComponent component. Even if the object’s properties change, React.PureComponent will not detect the change and will not re-render the component.

To address this limitation, it is important to ensure that the props and state are passed to React.PureComponent is passed by values and not complex objects/arrays passed by references.

• Only Compares Props and State: React.PureComponent only compares the component’s props and state to determine whether a re-render is necessary. It does not take into account other factors that may affect the rendering of the component, such as changes to the context or changes to the parent component.

import React from 'react';

class MyComponent extends React.PureComponent {
  render() {
    return <div>{this.context.someValue}</div>;
  }
}

MyComponent.contextType = MyContext;

const App = () => {
  return (
    <MyContext.Provider value={{ someValue: 'Hello World' }}>
      <MyComponent />
    </MyContext.Provider>
  );
};

In this example, the MyComponent component uses the context to render its content. If the context value changes, React.PureComponent will not detect the change and will not re-render the component.

To address this limitation, it may be necessary to use shouldComponentUpdate() instead of React.PureComponent to implement a more custom comparison logic that takes into account all the factors that may affect the rendering of the component.

Improve React App Performance Using React.memo()

React.memo() is a higher-order component provided by React that can be used to optimize the rendering of functional components. It is similar to React.PureComponent in that it implements a shouldComponentUpdate() method to reduce unnecessary re-renders, but it is designed for use with functional components instead of class components.

How to use React.memo()?

React.memo() works by memoizing the result of a component’s render method based on its props. Memoization is the process of caching the result of a function call based on its input. By memoizing the result, React.memo() can determine whether a re-render is necessary based on the changes to the props, reducing the number of unnecessary re-renders and improving the performance of the component.

import React from 'react';

const MyComponent = React.memo((props) => {
  return <div>{props.someProp}</div>;
});

In this example, we use React.memo() to wrap our functional component and memoize its result based on its props. The component will only re-render if the someProp prop has changed, reducing the number of unnecessary re-renders.

React.memo() can also accept a second argument, a comparison function that can be used to customize the comparison of the previous and next props. The comparison function should return true if the props are equal and false if they are not.

import React from 'react';

const MyComponent = React.memo((props) => {
  return <div>{props.someProp}</div>;
}, (prevProps, nextProps) => {
  return prevProps.someProp === nextProps.someProp;
});

In this example, we use a comparison function to compare the previous and next someProp props. If the props are equal, the component will not re-render. If the props are not equal, the component will re-render.

It is important to note that React.memo() only performs a shallow comparison of the props. This means that it only compares the references of the props, not their contents. If the props contain complex objects or arrays, React.memo() will not detect changes to their contents, resulting in unnecessary re-renders.

Other React Techniques for Performance

In addition to the techniques we have discussed, there are several other strategies that can be used to optimize the performance of a React application.

• Server-side rendering (SSR): Server-side rendering is a technique used to improve the initial load time of a web application by rendering the initial HTML on the server instead of the client. This can improve the performance of the application by reducing the time it takes for the user to see the initial content of the page.

To implement server-side rendering in a React application, we can use libraries such as Next.js or Razzle. These libraries provide tools and frameworks for building server-rendered React applications.

• Lazy loading: and code splitting Lazy loading and code splitting are techniques used to improve the performance of large applications by only loading the code that is necessary for a given page or feature. This can reduce the size of the initial bundle and improve the page load time.

React provides tools and APIs for implementing lazy loading and code splitting. We can use the dynamic import() function to load components or modules lazily, meaning that they will only be loaded when they are needed.

import React, { lazy, Suspense } from 'react';

const LazyComponent = lazy(() => import('./LazyComponent'));

function App() {
  return (
    <div>
      <Suspense fallback={<div>Loading...</div>}>
        <LazyComponent />
      </Suspense>
    </div>
  );
}

In this example, we use the lazy() function to load a component lazily, meaning that it will only be loaded when it is needed. We also use the Suspense component to show a loading spinner while the component is being loaded.

• Using Web Workers: Web Workers are a browser API that allows for running JavaScript code in a separate thread, improving the performance and responsiveness of the application by offloading expensive computations to a separate thread.

In React, we can use Web Workers to perform expensive calculations, such as image processing or data analysis, without blocking the main thread.

const worker = new Worker('./worker.js');

worker.onmessage = (event) => {
  console.log(`Result: ${event.data}`);
};

worker.postMessage(42);

In this example, we create a new Web Worker using the Worker() constructor and listen for messages from the worker using the onmessage event handler. We can send messages to the worker using the postMessage() method.

Tools for Improving React Performance

To optimize the performance of a React application, it is important to use performance tools that can help identify performance issues and areas for improvement. There are several performance tools available for React that can help developers to monitor, profile, and analyze the performance of their application.

• React Developer Tools: React Developer Tools is a browser extension that provides tools and features for debugging and profiling React applications. It allows developers to inspect and modify the component hierarchy, view component props and state, and analyze the performance of the application.

• Profiling and debugging tools: There are several profiling and debugging tools available for React that can help developers to identify and fix performance issues. These tools can be used to identify slow components, inefficient rendering, and other performance issues.

React Profiler

One such tool is the React Profiler, which is a built-in tool provided by React. It allows developers to measure the performance of their application and identify components that are causing performance issues.

import React from 'react';
import { unstable_trace as trace } from 'scheduler/tracing';

const App = () => {
  return <div>Hello World</div>;
};

trace('initial render', performance.now(), () => {
  ReactDOM.render(<App />, document.getElementById('root'));
});

In this example, we use the unstable_trace() method from the scheduler/tracing module to measure the performance of the initial render of the App component. We can then use the React Profiler to analyze the performance of the application and identify any performance issues.

• Performance metrics and benchmarks: These tools can measure a React application’s performance and identify improvement areas. These metrics can include page load time, time to interact, and time to the first byte.

One such tool is PageSpeed Insights, which is a performance auditing tool provided by Google. It allows developers to measure the performance of their application and identify areas for improvement.

Best Practices

Best practices for performance optimization

• Use React.PureComponent or React.memo() to reduce unnecessary re-renders.

• Use server-side rendering and code splitting to improve the initial load time of the application.

• Use container components to separate the responsibility of fetching and managing data from the responsibility of rendering the data.

• Use performance tools, such as React Developer Tools and profiling and debugging tools, to monitor and analyze the performance of the application.

Common pitfalls to avoid

• Performing expensive computations in the render method.

• Using complex objects or arrays as props or state.

• Not using lazy loading or code splitting to reduce the size of the initial bundle.

• Not optimizing images or other media assets for the web.

Conclusion

React is a powerful and versatile framework for building user interfaces, but performance can become a critical issue as the size and complexity of a React application grow. There are several techniques and tools available for optimizing the performance of a React app, including the use of React.PureComponent and React.memo() to reduce unnecessary re-renders, server-side rendering, and code splitting to improve the initial load time of the application, and container components to separate the responsibility of fetching and managing data from the responsibility of rendering the data.

Additionally, there are several other techniques that can be used to optimize the performance of a React application, including lazy loading, using Web Workers and optimizing media assets for the web. By using these techniques in conjunction with performance tools, such as React Developer Tools and profiling and debugging tools, developers can identify performance issues and areas for improvement, and optimize the performance of their React application.

However, it is important to be aware of common pitfalls to avoid when optimizing the performance of a React application, such as performing expensive computations in the render method and using complex objects or arrays as props or state.