Top 10 React Performance Optimization Techniques [React Interview]

Performance optimization of a react application is necessary while building any react application, there are many performance optimization techniques exist to improve performance using the JavaScript, CSS or network optimization side, but in this post we primarily focused on the performance optimization techniques which we can use specific to React codebase and patterns. Let's checkout these top 10 and bonus React performance optimization techniques

Table of content

• Memoization using Rect.memo()
• Control re-render using PureComponent or shouldComponentUpdate
• Use Virtualized Lists for Efficient Rendering
• Code Splitting using React.lazy()
• Memoize Expensive Computations with useMemo() hook
• Use unique and stable keys for the list
• Optimize Context Consumers with useContext()
• Avoid re-rendering inline functions using useCallback() hook
• Implement Debouncing and Throttling for User Input
• Cleanup asynchronous task on un-mount inside useEffect() hook
• Some More React Performance Optimization Techniques
• Final Thoughts
• Learn Next

1. Memoization using React.memo()

React.memo is a higher-order component that memoizes the functional component props. It prevents unnecessary re-renders by comparing the previous and current props

In the below example, Child is wrapped in React.memo() so

• ✅ It re-renders only when count changes.
• ❌ It skips re-render when only text changes and return the Memoized component.

import React, { useState } from "react";

// Child Component
const Child = React.memo(({ count }) => {
  console.log("Child rendered!");
  return <h2>Child Count: {count}</h2>;
});

// Parent Component
function Parent() {
  const [count, setCount] = useState(0);
  const [text, setText] = useState("");

  return (
    <div>
      <Child count={count} />

      <button onClick={() => setCount((c) => c + 1)}>Increment Count</button>

      <input
        value={text}
        onChange={(e) => setText(e.target.value)}
        placeholder="Type something"
      />
    </div>
  );
}

export default Parent;

2. Control Re-render using PureComponent or shouldComponentUpdate

Use PureComponent or shouldComponentUpdate to specify when the component should be re-rendered by shallow comparison of props.

class MyComponent extends React.PureComponent {
   // Component logic here
} 

3. Use Virtualized Lists for Efficient Rendering

When working with large lists, consider using virtualized list (library like react-virtualized or react-window) to render only the visible items in the viewport, that improves performance significantly by just allowing the visible part in the DOM

4. Code Splitting using React.lazy()

Split your application into smaller chunks using dynamic imports or React.lazy to load components only when needed, reducing the initial bundle size and improving load times. Use Suspense to show the fallback option while modules are lazy loaded. Checkout the below example

import React, { Suspense, lazy, useState } from "react";

// Lazy load the components
const Home = lazy(() => import("./Home"));
const About = lazy(() => import("./About"));

function App() {
  const [page, setPage] = useState("home");

  return (
    <div>
      <button onClick={() => setPage("home")}>Home</button>
      <button onClick={() => setPage("about")}>About</button>

      {/* Suspense shows fallback while component is loading */}
      <Suspense fallback={<p>Loading...</p>}>
        {page === "home" ? <Home /> : <About />}
      </Suspense>
    </div>
  );
}

export default App;

5. Memoize Expensive Computations with useMemo() hook

React's useMemo hook allows you to memoize expensive computations and calculations, ensuring that they are only re-executed when dependencies change. Learn More about skipping re-rendering using useMemo

import React, { useState, useMemo } from "react";

function ExpensiveCal() {
  const [count, setCount] = useState(0);
  const [text, setText] = useState("");

  // Expensive computation
  const expensiveValue = useMemo(() => {
    console.log("Doing Expensive calculation...");
    let total = 0;
    for (let i = 0; i < 1000000000; i++) {
      total += i;
    }
    return total + count;
  }, [count]); // ✅ Only re-run when "count" changes

  return (
    <div>
      <h2>Expensive Value: {expensiveValue}</h2>
      <button onClick={() => setCount((c) => c + 1)}>Increment Count</button>

      <input
        value={text}
        onChange={(e) => setText(e.target.value)}
        placeholder="Type something..."
      />
    </div>
  );
}

6. Use unique and stable keys for the list

React uses keys to optimize the rendering of the component, so use unique and stable keys whenever rendering any list of elements helps react to improve rendering. Avoid using index and random function to generate keys.

import React from "react";

function UserList() {
  const users = [
    { id: 1, name: "FrontendGeek" },
    { id: 2, name: "Anuj" },
    { id: 3, name: "Sharma" },
  ];

  return (
    <ul>
      {users.map((user) => (
        <li key={user.id}> // ✅Unique Key
             {user.name}
        </li>
      ))}
    </ul>
  );
}

7. Optimize Context Consumers with useContext()

Instead of multiple context consumers, use the useContext hook to subscribe to a context provider, reducing the number of re-renders and improving performance.

import React, { createContext, useContext } from "react";

const ThemeContext = createContext();
const UserContext = createContext();

function Profile() {
  const theme = useContext(ThemeContext);
  const user = useContext(UserContext);

  return (
    <div style={{ background: theme.background, color: theme.text }}>
      <h2>User: {user.name}</h2>
    </div>
  );
}

export default function App() {
  const theme = { background: "black", text: "white" };
  const user = { name: "FrontendGeek" };

  return (
    <ThemeContext.Provider value={theme}>
      <UserContext.Provider value={user}>
        <Profile />
      </UserContext.Provider>
    </ThemeContext.Provider>
  );
}

8. Avoid re-rendering inline functions using useCallback() hook

Inline function as part of the react functional component redeclared every time when component renders, wrapping up the function with useCallback hook preserves the function reference and thats why there is no need to re-declare function on every render.

Even avoid using the inline function calls on the events directly as part of the component itself

import React, { useState, useCallback } from "react";

const Child = React.memo(({ onClick }) => {
  console.log("Child rendered");
  return <button onClick={onClick}>Click Me</button>;
});

function Parent() {
  const [count, setCount] = useState(0);
  const [text, setText] = useState("");

  // ✅ useCallback memoizes the function reference
  const handleClick = useCallback(() => {
    console.log("Button clicked");
  }, []); // no dependencies, return same function reference always

  return (
    <div>
      <Child onClick={handleClick} />
      <p>Count: {count}</p>
      <button onClick={() => setCount((c) => c + 1)}>Increment Count</button>
      <input
        value={text}
        onChange={(e) => setText(e.target.value)}
        placeholder="Type something"
      />
    </div>
  );
}

9. Implement Debouncing and Throttling for User Input

Debounce or throttle user input events using libraries like lodash or custom implementations to control the frequency of function executions, improving performance in data-heavy applications.

learn more about Debouncing & Throttling 

10. Cleanup asynchronous task on un-mount inside useEffect() hook

Always clean up any asynchronous task when the component is unmounted such as setTimeout or setInterval to reduce the memory consumption and avoid memory leakage which can lead to performance issues if keep going for a extended duration.

import React, { useEffect, useState } from "react";

function TimerComponent() {
  const [time, setTime] = useState(0);

  useEffect(() => {
    const interval = setInterval(() => {
      setTime((t) => t + 1);
    }, 1000);

    // Cleanup interval on unmount
    return () => {
      clearInterval(interval);
      console.log("Timer cleaned up");
    };
  }, []);

  return <div>Time: {time}</div>;
}

Some More React Performance Optimization Techniques

# Use Ref instead of state when necessary

Change in dynamic data where we doesn't requires update in any part of the react component than its better to store that data in ref instead of state. If you store as part of the state it will re-render the react component but since there is no change required it's totally waste.

# Dependency optimization

Avoid importing directly from the root this will help you to keep only the required modules from the library which you are using in your application and it helps to keep the minimal bundle size -> Faster bundle loading -> faster react application, for example

import {get} from 'lodash ❌

import get from 'lodash/get' ✅

# Avoid spread props

As props can change anytime, only use props that you need, and don’t add those that are not required.

Final Thoughts

There are many more optimization techniques can be used for specific applications but here we have covered the most common react performance optimization techniques only. Understanding Implementing these React performance optimization techniques can significantly enhance the speed and responsiveness of your React applications.

By leveraging memoization, lazy loading, virtualization, and other best practices, you can create high-performing optimized React applications.

Further Reading

1. 100+ Top React JS Interview Questions and Answers
2. 20 Most Asked Custom Hooks in React
3. Best resources to prepare for react interview