What are the best techniques for performance optimization in React?

Optimization of React applications includes a variety of strategies to help improve application speed and responsiveness:

1. Memoization

Storing the results of expensive calculations in memory and reusing them if the input data has not changed. This is especially useful for optimizing the rendering of components that often receive the same data.

2. List virtualization

Displaying only those list elements that are currently visible in the view. This technique significantly reduces the number of elements rendered in the DOM and improves performance with large data sets.

3. Lazy Loading of images and components

Delayed loading of resources until the user needs them. This helps reduce the initial page load time.

4. React Fragments

Eliminating unnecessary DOM elements, leading to more efficient rendering. This is especially useful when you want to avoid redundant HTML elements.

5. Code Splitting

Splitting the application into smaller parts (chunks) that are loaded when needed. This makes the application load faster, and users do not have to wait to download all the code at the start.

How does the virtual DOM mechanism work in React and how does it affect performance?

The virtual DOM is one of the foundations of performance in React. It acts as an intermediate layer that enables faster and more efficient operations on the DOM. The virtual DOM is basically a simplified representation of the real DOM that stores information about the structure of components.

The main advantage of the virtual DOM is that when the state of the application changes, React does not immediately update the entire real DOM. Instead, it compares (diffing) the new version of the virtual DOM with the previous one and updates only those elements of the real DOM that have changed. This makes DOM operations more efficient and faster, reducing browser load and improving application performance.

What are the best ways to avoid unnecessary component renders?

Avoiding unnecessary component renders is one of the most important tasks when optimizing a React application. In React, we have several tools that can help with this:

1. React.memo() – this is a higher function component (HOC) that remembers the result of a component render and reuses it if the props have not changed.

Example:

jsx

   import React, { Suspense, lazy } from

 'react';

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

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

2. lazy loading images – load images only when the user approaches them in the view. This can be done using the react-lazyload library.

Example:

jsx
   import LazyLoad from 'react-lazyload';

   const LazyImage = ({ src, alt }) => (
     <LazyLoad height={200} offset={100}>
       <img src={src} alt={alt} />
     </LazyLoad>
   );

   export default LazyImage;

How to test and monitor React application performance?

Monitoring application performance is key to long-term success. Here are tools that can help with this:

1. React DevTools – use the component debugging tool to analyze component performance and see which components are rendered unnecessarily.

2. React profiling – use the profiling feature in React DevTools to see how long components take to render.

3. Google Lighthouse – a tool that measures the performance of web applications and gives tips for optimization.

How to use React.lazy() and Suspense to load components asynchronously?

Asynchronous component loading in React using React.lazy() and Suspense allows you to optimize your application by splitting your code and dynamically loading parts of it. As a result, the application loads faster and the user sees the interface sooner, before all the components are loaded. This functionality is especially useful in multi-page applications or where not all components are needed right away. Suspense allows you to display an alternate element (e.g., a spinner) while a component is loading, which improves the user’s experience by ensuring a smooth interaction.

Usage example:

jsx

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

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

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

In this example, the LazyComponent will be loaded dynamically, and while it is loading, the user will see a placeholder in the form of the text “Loading…”. This significantly improves the initial rendering time of the application and affects the overall performance.

How to optimize a React app for user interaction?

Optimizing an app for user interaction is crucial to ensure a smooth and responsive UI, especially in more complex apps. Unoptimized apps can lead to so-called “yank” – disruptions in animation fluidity and navigation that reduce the user experience. Here are techniques to help optimize user interactions and achieve smoother app performance.

1. Throttling i debouncing

Throttling i debouncing to techniki, które ograniczają częstotliwość wywołań funkcji w odpowiedzi na zdarzenia użytkownika, takie jak przewijanie, zmiana rozmiaru okna czy wpisywanie tekstu. Pomaga to zmniejszyć obciążenie procesora i uniknąć nadmiernych renderów.

Debouncing: the function is called after a certain period of inactivity. This is useful, for example, when optimizing the search function while typing text.

Example of debouncing:

jsx

  const debounce = (func, delay) => {
    let timeout;
    return (...args) => {
      clearTimeout(timeout);
      timeout = setTimeout(() => func(...args), delay);
    };
  };

  const handleInputChange = debounce((value) => {
    console.log(value);
  }, 300);

Throttling: limits the number of function calls to one in a set interval. Useful for optimizing events such as scrolling or window resizing.
Example of throttling:

jsx
  const throttle = (func, delay) => {
    let lastCall = 0;
    return (...args) => {
      const now = new Date().getTime();
      if (now - lastCall >= delay) {
        lastCall = now;
        func(...args);
      }
    };
  };

  const handleScroll = throttle(() => {
    console.log("Scrolled");
  }, 200)

2 CSS animations instead of JavaScript

Where possible, it’s a good idea to use CSS animations instead of JavaScript. CSS animations are usually more efficient because they can be handled by the GPU, which relieves the CPU and provides smoother performance, especially for more complex animations.
It is recommended to use CSS properties such as transform and opacity, which are effectively rendered on the GPU, which helps avoid CPU overload.

For example:

css

.element {
  transition: transform 0.3s ease-in-out;
}

.element:hover {
  transform: translateX(100px);
}

3 Achieve smoothness of animation

To ensure smooth animation, especially for complex applications, it’s a good idea to use will-change in CSS. This tells the browser which properties will be changed, so it can optimize their processing in advance. However, be sure to use this only where it is really needed, as excessive use of will-change can overload memory.

4 Optimize navigation events

User interactions, such as navigation between pages, can be optimized through techniques such as pre-fetching and code splitting. This ensures that the user experiences smooth navigation because the components or data they will need are loaded in the background before they are actually invoked.

5 Eliminating liquidity disruptions (aka “yank”)

Fluency interference (jank) can be caused by overloading the browser when performing tasks of high computational complexity (such as intensive DOM operations or rendering large amounts of data). The solution may be offloading these tasks using Web Workers or splitting larger tasks into smaller portions using functions such as requestIdleCallback or requestAnimationFrame.

Summary

Optimizing React applications involves a variety of techniques, from basic ones like memoization and lazy loading to more advanced ones like Concurrent Mode and Suspense for data. The key is to choose the right tools and techniques depending on the size and nature of the application, monitor performance, and constantly test the application for speed.

Finally, if you want to expand your knowledge of React and its optimization capabilities, it’s worth looking at the official React documentation : https://react.dev/