Landing your first React developer job can feel like a mountain to climb. You’re up against many smart folks. Employers want to see you truly grasp React’s core ideas. This article gives you a head start. We break down the 40 most asked React interview questions. Master these, and you will show you’re ready for a junior React role. Let’s get you prepared.

Section 1: Core React Concepts

What is React?

React is a free and open-source frontend JavaScript library. Facebook and a community of developers keep it updated. Its main job is to help you build user interfaces, often called UIs. Think of it as a tool for making interactive web pages. React lets you create big web apps out of small, reusable pieces.

Is it a library or a framework? React is a library. A framework offers a complete solution, but a library gives you tools for specific tasks. React helps with the “view” part of your app. It does not dictate how you manage data or route pages. This design makes React flexible. You can use it with other libraries for different needs. Its component-based approach is key. You build UIs using isolated, reusable bits of code. Each component handles its own part of the UI. This makes complex UIs easier to manage and update. React also uses a “declarative” style. You describe what you want the UI to look like, and React figures out how to make it happen. You don’t tell it every tiny step.

What is JSX, and why do we use it?

JSX stands for JavaScript XML. It’s a syntax extension for JavaScript. This means you can write HTML-like code right inside your JavaScript files. It may look like HTML, but it’s not. Browsers can’t read JSX directly. What happens then? Babel, a JavaScript compiler, changes your JSX code into regular JavaScript calls that React can understand.

Why use JSX? It makes writing React components much easier. You can see your UI structure and its logic in one place. This improves readability. Imagine building a UI with only plain JavaScript function calls; it would get messy fast. With JSX, you embed JavaScript expressions inside curly braces {}. This lets you put variables, functions, and even other React components directly into your UI structure. It’s a powerful way to mix UI and logic.

How does the Virtual DOM work in React?

The Virtual DOM is a key part of React’s speed. It’s a lightweight copy of the actual DOM. Think of the DOM (Document Object Model) as the tree structure representing your webpage. When you make changes in a React app, React first updates this Virtual DOM, not the real one. It builds a brand-new Virtual DOM tree.

Next, React compares the new Virtual DOM with the old one. This comparison is called “diffing.” React figures out exactly what changed, what was added, or what was removed. It finds the minimal number of changes needed. Then, it sends only these specific updates to the real DOM. This process is called “reconciliation.” Instead of re-rendering the whole page, which is slow, React only updates what’s necessary. This makes your React apps incredibly fast and efficient.

Explain Components and Props in React.

Components are the building blocks of any React application. They are independent, reusable pieces of code. Think of them like Lego bricks. Each brick has a specific purpose. You can put them together to build a complex structure. In React, components let you split the UI into smaller, manageable parts. This makes your code easier to organize and maintain.

There are two main types: functional components and class components. Functional components are simple JavaScript functions that return JSX. Class components are ES6 classes that extend React.Component and have a render() method.

Props (short for properties) are how you pass data from a parent component to a child component. They are like arguments passed to a function. Props are read-only; you cannot change them inside the child component. This immutability ensures data flows in one direction, making your app’s behavior predictable. For example, a UserCardcomponent might get a name prop and a profileImage prop to display user details. Be careful with “prop drilling.” This happens when you pass props through many layers of components that don’t actually need the data, just to get it to a deeply nested child.

What is State in React?

State is an object that holds data that might change over time within a component. It controls how a component behaves and what it renders. Think of state as a component’s memory. When the state changes, React re-renders the component to show the new data. This makes your UI dynamic and interactive.

For functional components, you manage state using the useState hook. You declare a state variable and a function to update it. For example, const [count, setCount] = useState(0); creates a count state variable starting at zero. In class components, state is an object called this.state. You update it using this.setState(). Always use the updater function or this.setState() to change state. Directly modifying state can lead to unexpected issues. You should use state when a component needs to keep track of information that changes and affects its rendering.

Explain Lifecycle Methods in Class Components.

Class components have special methods called lifecycle methods. These methods run at specific points during a component’s life. Think of a component’s life like a play with different acts.

• constructor(): This runs first when a component is created. It’s used for setting up initial state and binding methods.
• static getDerivedStateFromProps(): Called before every render, whether it’s an initial mount or an update. It’s for syncing state with props.
• render(): This is the only required method. It renders your component’s JSX to the screen. It should be a pure function.
• componentDidMount(): This runs right after the component first appears on the screen. It’s perfect for data fetching or setting up subscriptions.
• shouldComponentUpdate(nextProps, nextState): This method lets you optimize performance. If it returns false, React skips re-rendering the component and its children.
• componentDidUpdate(prevProps, prevState): This runs after the component updates and re-renders. Great for reacting to prop or state changes.
• componentWillUnmount(): This runs just before a component is removed from the DOM. Use it to clean up subscriptions or timers.
• getSnapshotBeforeUpdate(): Called right before changes are committed to the DOM. It captures information before the update.
• componentDidCatch(): Used for error handling. It catches errors within its child components.

What are React Hooks?

React Hooks are functions that let you “hook into” React state and lifecycle features from functional components. Before hooks, these features were only available in class components. Hooks were introduced in React 16.8. They changed how many people write React code.

Hooks make functional components more powerful. You no longer need to write a class component to have state or manage side effects. This means less code. Your components become easier to read. useState lets you add state to functional components. useEffect handles side effects, like data fetching, similar to componentDidMount or componentDidUpdate. useContext helps you use React’s Context API more easily. Hooks promote code reuse and make logic easier to share between components.

Section 2: Advanced React Concepts & Hooks

Deep Dive into the useEffect Hook.

The useEffect hook lets you perform side effects in functional components. Side effects are operations that affect things outside the component itself. Common side effects include data fetching, manual DOM changes, subscriptions, or setting up timers. useEffect combines the roles of componentDidMount, componentDidUpdate, and componentWillUnmountfrom class components.

Its basic syntax is useEffect(setup, dependencies). The setup function runs after every render. You can control when it runs by providing a dependencies array as the second argument. If the array is empty [], the effect runs only once after the initial render, like componentDidMount. If you omit the array, it runs after every render. If you include variables in the array, the effect runs only when those variables change.

Often, side effects need cleanup. For example, if you set up a subscription, you need to unsubscribe when the component unmounts to prevent memory leaks. The setup function can return another function. This returned function is the cleanup function. It runs before the component unmounts and before the effect runs again (if dependencies change).

How does useContext simplify state management?

The useContext hook provides a way to pass data through the component tree without having to pass props down manually at every level. This problem is known as “prop drilling.” Imagine you have data from a parent component that a deeply nested child component needs. Without useContext, you’d have to pass that data through every component in between, even if they don’t use it themselves. This makes your code messy.

useContext helps you avoid this. First, you create a context using React.createContext(). This creates a Provider and a Consumer component. The Provider wraps the part of your component tree that needs access to the context. It takes a value prop, which is the data you want to share. Any component inside the Provider can then consume this context. To consume the context in a functional component, you use the useContext hook. You pass the context object to useContext, and it returns the current context value. This allows you to access global state or shared data effortlessly.

When should you use the useReducer Hook?

The useReducer hook is an alternative to useState for managing state. It’s particularly useful for complex state logic. Think of situations where your state depends on the previous state. Also, it’s great when your state updates involve multiple sub-values. It’s similar to how Redux works but built right into React.

You use useReducer by calling useReducer(reducer, initialState). It returns the current state and a dispatchfunction. The reducer function takes the current state and an action as arguments. It then returns the new state based on the action. Actions are plain JavaScript objects that describe what happened, like { type: 'increment' }.

When would you choose useReducer over useState? If your state logic becomes too complex with useState or if many state updates are related, useReducer brings more structure. It centralizes state logic in one place (the reducer function). This makes it easier to test and understand. For simple state like a boolean toggle or a single counter, useState is perfectly fine. For more complex, multi-part state updates, useReducer shines.

Explain Custom Hooks in React.

Custom hooks are special JavaScript functions. Their names always start with use, like useSomething. They let you reuse stateful logic across different components. Think of them as a way to extract common behavior from components. This makes your code cleaner and more organized.

You create a custom hook by defining a function that uses other built-in hooks (like useState, useEffect, useContext). For example, you might create a useToggle hook that manages a boolean state, or a useFetch hook for handling data fetching logic.

Once defined, you can use your custom hook in any functional component. It works just like a built-in hook. Custom hooks help you avoid duplicating code. If you find yourself writing the same useState and useEffect logic in multiple places, that’s a sign you should probably create a custom hook. They make your codebase more maintainable.

What are Higher-Order Components (HOCs)?

Higher-Order Components (HOCs) are a pattern for reusing component logic. A HOC is a function that takes a component as an argument and returns a new component. It’s a way to enhance or wrap existing components with additional props or behavior. HOCs were a common pattern before hooks.

For example, you might have a withAuth HOC that adds authentication logic to any component you pass to it. Or a withLoading HOC that displays a loading spinner while data fetches. The HOC does not modify the input component or use inheritance. Instead, it composes the original component by wrapping it in another component. HOCs are useful for cross-cutting concerns like logging, authentication, or data fetching. With the advent of hooks, many use cases for HOCs are now handled more simply with custom hooks. However, you might still encounter HOCs in older codebases.

What is the Render Props pattern?

The render props pattern is another way to share code between React components. It involves a component with a prop that is a function. This function “renders” what the component should display. The component passes its internal state or logic to this function, and the function uses that data to render JSX.

For example, a DataSource component might fetch data. Instead of rendering specific UI, it accepts a render prop. This prop is a function. DataSource calls this function, passing the fetched data as an argument. The consumer of DataSourcethen defines how to display that data by providing the render function.

Render props provide more flexibility than HOCs in some cases. You can compose them more easily. They also don’t suffer from “wrapper hell,” where components get nested too deeply with HOCs. While custom hooks are now often preferred for logic reuse, render props remain a valid and powerful pattern for component composition.

Section 3: State Management

Local State vs. Global State.

In React, state can be managed at different levels. Understanding the difference between local and global state is crucial for building scalable apps.

Local state, or component-level state, is data managed entirely within a single component. Only that component can access and modify it. For example, a counter component’s count state is local. If a dropdown menu’s isOpen state is managed only by that dropdown, it’s local. useState is the primary hook for managing local state. Use local state when the data is only relevant to one component and doesn’t need to be shared with its siblings or parents.

Global state, or application-level state, is data that needs to be shared across many components in different parts of your application. Think of user authentication status, theme settings, or items in a shopping cart. This data isn’t tied to one specific component. When multiple components need to access or modify the same piece of data, it should be global. React’s Context API is a built-in way to manage simpler global state. For very complex global state, external libraries like Redux are popular.

What is Prop Drilling, and why is it a problem?

Prop drilling is a common issue in React applications. It happens when you pass data (props) down through multiple nested components. Many of these components do not actually need the data themselves. They only pass it along to a child component further down the tree. Imagine giving a package to your neighbor, who then gives it to their neighbor, just to get it to someone three houses down.

This becomes a problem for several reasons. First, it makes your code harder to read and understand. You have to trace the prop through many components to see where it comes from and where it’s used. Second, it hurts maintainability. If you need to change the prop’s name or structure, you might have to update every intermediate component that passes it down. Third, it can make refactoring difficult. It tightly couples components that otherwise might be independent. While not strictly a performance issue, it certainly impacts developer experience. Solutions like the Context API or state management libraries help avoid prop drilling.

How does Context API help with state management?

React’s Context API provides a way to share data that can be considered “global” for a tree of React components. It lets you avoid passing props down manually at every level of the component tree. This directly addresses the prop drilling problem.

To use it, you first create a Context object using React.createContext(). This object comes with a Provider and a Consumer. The Provider component is wrapped around the part of your component tree that needs access to the shared data. It accepts a value prop, which is the data you want to make available. Any component within the Provider‘s subtree can then access this value. In functional components, you consume the context using the useContext hook. You just pass your context object to useContext, and it returns the current context value. This allows you to easily share things like theme preferences, user authentication status, or language settings across your app without explicit prop passing. While great for simpler global state, for very complex state management, dedicated libraries might be more suitable.

Explain Redux Fundamentals.

Redux is a popular, predictable state container for JavaScript applications. It’s often used with React for managing global application state. Redux follows a strict “unidirectional data flow.” This means data moves in one direction, making state changes easy to track.

Redux has three core principles:

1. Single Source of Truth: Your entire application’s state is stored in a single JavaScript object within one “store.” This makes it easy to debug and maintain.
2. State is Read-only: The only way to change the state is by emitting an “action.” An action is a plain JavaScript object describing what happened, like { type: 'ADD_ITEM', payload: { id: 1, name: 'Milk' } }.
3. Changes are Made with Pure Functions: To specify how the state changes in response to actions, you write “reducers.” Reducers are pure functions that take the current state and an action, then return a new state. They must not modify the original state.

When an action is dispatched, the reducer processes it, creates a new state, and updates the store. Components connected to the store automatically re-render with the new state. Redux helps manage complex state that needs to be shared by many components, providing a structured and debuggable way to handle it.

Mention other popular state management libraries besides Redux.

While Redux is a long-standing choice for state management in React, the ecosystem has many other options. These alternatives often aim for simpler setups or focus on specific use cases.

Zustand is a small, fast, and scalable state management solution. It’s known for being very lightweight and having a simple API. You create a store, and components can subscribe to parts of it. It works without needing context providers, making it very easy to integrate.

Recoil is developed by Facebook. It offers a unique approach using “atoms” and “selectors.” Atoms are units of state that components can subscribe to. Selectors are pure functions that transform atom state. Recoil integrates very well with React’s concurrency features. It’s designed to scale for large applications while being easy to use.

Other options include MobX, Jotai, and Valtio. Each library has its own philosophy and advantages. The best choice depends on your project’s needs and your team’s preferences.

Section 4: Routing and Navigation

Overview of React Router.

React Router is a standard library for handling routing in React applications. In single-page applications (SPAs) built with React, the browser doesn’t reload the entire page when you navigate. Instead, React Router manages changes to the URL. It then renders the appropriate components based on that URL.

It enables “client-side routing.” This means the routing logic runs directly in your browser, not on a server. React Router uses a “declarative” approach. You declare what routes your application has and which components should render for those paths. This makes navigation intuitive. It handles everything from simple page changes to complex nested views. React Router ensures your application feels like a traditional multi-page website, even though it’s an SPA.

How do you configure routes in React Router?

Configuring routes in React Router involves defining which component should render for a given URL path. The core components for this are BrowserRouter, Routes, and Route.

First, you wrap your entire application (or the part that needs routing) with BrowserRouter. This component uses the HTML5 history API to keep your UI in sync with the URL. Inside BrowserRouter, you use the Routes component. Routes acts like a switch statement. It renders the first <Route> that matches the current URL.

Each individual route is defined using the Route component. A Route takes a path prop, which is the URL path it should match, and an element prop, which is the React component to render when the path matches. For example, <Route path="/about" element={<AboutPage />} /> tells React Router to render the AboutPage component when the URL is /about. You can define multiple Route components within Routes to cover all your application’s paths.

Explain Dynamic Routing.

Dynamic routing in React Router allows you to create routes that capture variable parts of the URL. These variable parts are called URL parameters. Imagine an e-commerce site where each product has a unique ID. You don’t want to create a separate route for every single product. Dynamic routing solves this.

You define a dynamic segment in your route’s path by prefixing it with a colon (:). For example, a route like <Route path="/products/:productId" element={<ProductDetail />} /> would match URLs like /products/123 or /products/abc. The :productId part is a URL parameter.

Inside the ProductDetail component, you can access the value of this URL parameter using the useParams hook from react-router-dom. useParams returns an object where keys are the parameter names (e.g., productId) and values are the actual values from the URL (e.g., 123 or abc). This allows you to fetch and display specific data based on the URL.

How do you implement Nested Routing?

Nested routing lets you render components within other components based on their relative paths. It’s useful for creating complex UI layouts where a parent component always shows certain content, and its children show varying content based on deeper URL segments. Think of a dashboard with a sidebar: the sidebar stays, but the main content area changes.

In React Router, you define nested routes by placing Route components inside another Route component. The parent Route‘s path acts as a base. Child routes then define paths relative to this parent path. For example:

<Route path="/dashboard" element={<DashboardLayout />}>
  <Route path="overview" element={<DashboardOverview />} />
  <Route path="settings" element={<DashboardSettings />} />
</Route>

Here, /dashboard/overview will render DashboardOverview inside DashboardLayout. To render the child route’s element, the parent component (DashboardLayout in this example) must use the Outlet component from react-router-dom. Outlet acts as a placeholder where child routes will render. This pattern is great for creating consistent layouts that adapt to different sub-pages.

How can you achieve Programmatic Navigation in React Router?

Programmatic navigation means changing the URL and navigating to a new route using JavaScript code, instead of clicking a Link component. This is often needed after a form submission, a successful API call, or in response to some user action not tied to a direct link.

In modern React Router, you achieve this using the useNavigate hook. You call useNavigate() inside your functional component, and it returns a navigate function. You then call this navigate function with the path you want to go to.

For example, after a user logs in successfully, you might want to redirect them to their dashboard.

import { useNavigate } from 'react-router-dom';

function LoginForm() {
  const navigate = useNavigate();

  const handleSubmit = async (event) => {
    event.preventDefault();
    // ... handle login logic
    const success = await loginUser(formData);
    if (success) {
      navigate('/dashboard'); // Navigate to the dashboard
    }
  };

  return (
    // ... form JSX
  );
}

The navigate function can also take a second argument, an options object, to replace the current entry in the history stack (instead of pushing a new one) or pass state.

Section 5: Styling and Performance

Discuss different styling approaches in React.

React offers many ways to style your components. Choosing one often depends on project size and team preference.

CSS Modules solve the problem of global CSS. Each CSS file becomes a module. All class names inside it are automatically scoped to that component. This means class names like .button in one component won’t conflict with a .button in another. You import CSS files like JavaScript modules.

Styled Components is a popular library for “CSS-in-JS.” You write actual CSS code inside your JavaScript files, using tagged template literals. It creates unique class names for your styles and injects them into the DOM. This ties styles directly to components.

Inline Styles are JavaScript objects applied directly to elements using the style prop. For example, <div style={{ color: 'blue', fontSize: '16px' }}>Hello</div>. They’re good for dynamic styles but can be verbose for complex layouts.

Tailwind CSS is a utility-first CSS framework. Instead of writing custom CSS, you apply pre-defined utility classes directly in your JSX, like <button className="bg-blue-500 text-white font-bold py-2 px-4 rounded">Click me</button>. It promotes rapid UI development. Each approach has pros and cons for scalability and maintainability.

What are some React performance optimization techniques?

Optimizing React app performance keeps users happy. Several techniques can make your application faster and smoother.

React.memo is a higher-order component that memoizes functional components. It prevents a functional component from re-rendering if its props have not changed. Wrap your component like export default React.memo(MyComponent);. This saves unnecessary re-renders.

useCallback memoizes functions. It returns a memoized version of a callback function that only changes if one of its dependencies has changed. This is useful when passing callbacks to optimized child components to prevent them from re-rendering.

useMemo memoizes values. It computes a value only when one of its dependencies changes. Use it for expensive calculations that don’t need to run on every render. const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);

Code splitting and lazy loading improve initial load times. Instead of loading your entire app’s code at once, you split it into smaller bundles. React.lazy() lets you render a dynamic import as a regular component. Combine it with Suspenseto show a fallback (like a loading spinner) while the component loads. These techniques reduce the amount of JavaScript the browser needs to download and parse upfront.

Why are Keys important when rendering lists in React?

The key prop is vital when you render a list of elements in React. Whenever you create a list of components or elements, like using map() on an array, React asks for a unique key for each item.

key helps React identify which items in the list have changed, been added, or been removed. When a list re-renders, React uses the key to match items in the old list with items in the new list. Without stable keys, React might update the wrong items. This can lead to unexpected behavior, bugs, or performance issues. Imagine a list of tasks. If you delete a task in the middle, without proper keys, React might just update the content of the wrong element instead of removing the correct one and re-ordering.

The best practice for a key is to use a unique and stable identifier for each item. This means an ID from your data source is perfect. Avoid using array indexes as keys if the list items can be reordered, added, or removed, as this can cause problems.

Explain Debouncing and Throttling in React.

Debouncing and throttling are techniques to control how often a function runs. They’re very useful for optimizing performance, especially with frequently triggered events like typing in a search bar or scrolling.

Debouncing delays the execution of a function until a certain amount of time has passed since the last time the event was fired. If the event fires again before the delay is over, the timer resets. Imagine a search input: you don’t want to make an API call for every single keystroke. With debouncing, the search function only runs after the user pauses typing for, say, 500 milliseconds. If they keep typing, the previous timer is cancelled.

Throttling limits how often a function can run within a given time period. It ensures a function runs at most once in a specified interval. Think of a scroll event: you might not need to update something on every single pixel scroll. Throttling ensures the scroll handler runs only every, for example, 200 milliseconds, no matter how fast the user scrolls.

Both techniques reduce the number of times expensive operations are performed, improving your app’s responsiveness and saving resources. You typically implement these using utility functions or libraries that wrap your event handlers.

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Section 6: Testing and Deployment

What is Unit Testing in React, and what tools are used?

Unit testing focuses on testing individual, isolated parts of your code. In React, this means testing components in isolation. You want to make sure each component renders correctly given specific props or state. You also want to check if it behaves as expected when users interact with it.

The most common tools for unit testing React components are Jest and React Testing Library. Jest is a JavaScript testing framework. It provides assertion methods (like expect().toBe()) and a test runner. React Testing Library is built on top of Jest. It encourages testing components in a way that mimics how users would interact with them. It queries the DOM nodes rather than testing component internals.

What should you test? You might check if a button click calls a specific function. You can verify if text appears on the screen when a component mounts. Or you can confirm if a component updates correctly after a state change. Basic assertions involve checking if elements exist, if text content is correct, or if certain attributes are present.

Explain Integration Testing in React.

Integration testing goes beyond unit testing. It verifies that different parts of your application work together correctly. In React, this often means testing the interaction between multiple components. You’re checking how components communicate with each other.

For example, you might test a parent component that renders several child components. You want to ensure that actions in one child component correctly trigger updates in another or in the parent. Or you might test a form that uses several input components and a submission button. You’d fill out the inputs and click submit, then check if the form’s submission logic works as expected. React Testing Library is also excellent for integration testing. It allows you to render larger parts of your application and simulate user interactions, making sure the flow between components is smooth and correct.

Briefly mention End-to-End (E2E) Testing.

End-to-End (E2E) testing simulates a real user’s journey through your entire application. It tests the complete flow, from the user interface down to the database and back. The goal is to ensure that the whole system works together as intended.

For a React app, an E2E test might involve navigating through several pages, filling out forms, clicking buttons, and verifying that the final result appears correctly. These tests run in a real browser environment. Popular E2E testing frameworks include Cypress and Playwright. While unit and integration tests focus on smaller parts, E2E tests provide confidence that your entire application is functioning from the user’s perspective.

Discuss Common Deployment Strategies for React applications.

Once your React application is ready, you need to deploy it so users can access it. Several common strategies exist.

Static Site Hosting is the most common for client-side rendered React apps. After building your app (which creates static HTML, CSS, and JavaScript files), you host these files on a web server. Services like Netlify and Vercel are incredibly popular for this. They offer continuous deployment directly from your Git repository. Every time you push code, they automatically rebuild and deploy your app. This method is simple, fast, and cost-effective for most React projects.

Server-Side Rendering (SSR) or Static Site Generation (SSG) involves a Node.js server. Frameworks like Next.js or Remix use this. Instead of sending an empty HTML file and letting React build the content in the browser, the server renders the initial HTML for your React components. This improves initial load performance and SEO. You deploy these applications to a server environment that can run Node.js, often using services like Vercel, Netlify, or traditional cloud providers.

Conclusion

You have now explored the 40 most asked React interview questions for freshers. We covered everything from core React concepts like JSX and the Virtual DOM to advanced hooks, state management patterns, and crucial deployment strategies. Understanding these topics will greatly boost your confidence.

Remember, truly mastering these concepts means more than just memorizing answers. Try to explain them in your own words. Build small projects that use these ideas. Practice answering questions out loud. Your hands-on experience and clear explanations will impress hiring managers. Keep learning, keep building, and good luck with your interviews!

Frequently Asked Questions (FAQ)

What is the primary difference between a library and a framework in JavaScript?

A library gives you tools to solve specific problems in your code, like React for UI. You call the library’s functions. A framework provides a complete structure for your app. It dictates how you build things, often calling your code when certain events happen. Think of it: you call a library, but a framework calls you.

How does React ensure performance with its Virtual DOM?

React improves performance by using a Virtual DOM, which is a lightweight copy of the real DOM. When state changes, React first updates this Virtual DOM. It then compares the new Virtual DOM with the old one (the “diffing” process). React identifies only the exact changes needed. Finally, it applies only these minimal updates to the actual browser DOM. This avoids costly full page re-renders.