In the fast-paced world of web development, React has emerged as a popular library for building user interfaces. Mastering react coding interview questions is essential for developers looking to excel in technical interviews. This article provides a comprehensive overview, including basic concepts, common questions, and tips for success.
React is a JavaScript library developed by Facebook to create dynamic web applications. It enables developers to create reusable UI components, efficiently manage state, and update the user interface effectively. Understanding the core principles of React, such as components, props, state, and lifecycle methods, is crucial for react interview coding questions.
React is a library for creating user interfaces using JavaScript, mainly single-page applications. It adheres to a component-based approach, through which the UI components with their own state can be created by the developers in reusable manner.
Components are lightweight, reusable, and modular UI components that bear the UI as well as the code to control the UI. Components may be class components or functional components. Class components update their state and lifecycle using methods, whereas functional components use hooks for the same. This framework makes the code easier to maintain, it is scalable, and allows for better coordination among the developers.
JSX is a syntax extension that allows developers to write HTML-like code natively within JavaScript. JSX improves the readability of code and allows for a more visual representation of the structure of the UI within code. JSX is transpiled into JavaScript function calls that actually render React elements, and it is one of the most widely used methods for constructing UIs in React.
Lifecycle hooks are special hooks in class components by which developers can hook into critical points in a component's lifecycle, i.e., mounting, updating, or unmounting. For instance, componentDidMount() is utilized for tasks such as fetching data once the component has been inserted into the DOM. It is the equivalent of most developers transitioning from class components to function components utilizing hooks such as useEffect() for handling side effects.
A state in react is an object that stores dynamic data in a react component. They are immutable and passed parent to child. It is handled internally and adjusts responses to user input or events. When state changes, react re-renders the component for the changes to be seen in the UI, which is crucial in interactive application development.
The useEffect() hook is important when handling side effects in functional components. It helps developers run things such as data fetching or subscription on each re-render or depending on some dependencies. Side-effect code that is separated from the rendering code results in clean and maintainable code.
Redux is a library for state management and is most typically employed with React to administer complicated app states. It keeps the state in a single store to leverage actions, and reducers to update that state. This systematical method makes global state administration easier and also easier to debug, particularly in more complicated applications.
Context enables data to be passed along the component tree without having to do so manually at each step. It is particularly suitable for theme or authentication status-like global values. Data can be encapsulated and exposed as context with a context provider so that any component that requires it can use it without support being unmanageable.
Error boundaries are components that capture JavaScript errors from their child components, allowing the user interface to degrade smoothly. They enable developers to display fallback UIs or log errors, preventing the entire application from crashing and enhancing the user experience.
Server-side rendering (SSR) is a technique where the server renders the initial HTML of a React application. This improves performance and SEO by providing fully rendered pages to users quickly, reducing the time to enhance the user experience, especially on slower networks.
The useMemo hook is used to optimize performance in functional components by memoizing expensive calculations. It returns a memoized value that is recalculated only when its dependencies change, preventing unnecessary recalculations during re-renders, which is beneficial for performance, especially with complex computations.
Prop drilling occurs when data is passed down through multiple layers of components, which can complicate the code and make it harder to manage. This often leads to a situation where a component needs to pass value in proportions to its child components just to get data to a deeper nested component. The Context API can help to solve these issues by allowing data to be shared directly among components without the need to pass react components through an interface.
Lazy loading can be implemented using react.lazy and Suspense to load components only when they are needed, improving initial load time and performance.
Fragments allow developers to group several elements without inserting extra nodes into the DOM. This helps to keep the DOM tree clean and optimize rendering.
API calls are normally done using the useEffect() hook to get data when a component mounts. This makes the component reflect the latest data from the server and cause updates depending on user interaction or state change. Async/await in useEffect() helps it to be easier to have cleaner, readable code if there is asynchronous action.
React DevTools is an extension for the browser that gives developers a means of viewing the React tree of components, optimizing the performance, and debugging the application more effectively. It enables one to view component props and state, profile the component rendering, and see updates, thus being a very useful tool in React development.
Primary key is required to assist React in determining which elements in a list have been added, updated, or deleted. Keys should be unique from one another and immutable so that it can offer optimal updates. Proper key usage optimizes performance by preventing unnecessary rendering so that React can efficiently handle DOM changes.
A higher-order component (HOC) is a function that returns a new component with additional behavior after passing a component as an argument. HOCs are used for a variety of concerns like fetching data, authentication, or logging. The pattern promotes code reuse since frequent behavior is separated from specific components.
The useReducer() hook is utilized for handling complicated logic in functional components. It is similar to Redux. The hook is very handy to handle state changes on the basis of various values or having intricate logic. With useReducer, one can have a properly organized and deterministic state management.
The useMemo hook is utilized to memoize expensive calculations and avoid re-renders when recalculations are unnecessary and improve performance.
The key prop is needed so that React can be notified about what things in a list have changed so that it can update them correctly and avoid unnecessary rendering.
React Fragment helps you to render a group of children without adding extra nodes to the DOM. It prevents unnecessary wrapper nodes, which keeps the markup cleaner and performance improved. You can also use <>.</> syntax for fragments.
PropTypes is one of the methods of validating prop types used when passing to a component. They prevent bugs by having correct data types and error messages during development mode.
Following is the comparison of React and Angular:
You can comment in React in two ways:
// This is a comment{/* This is a multi-line comment */}In Javascript, an arrow function is a concise way to write functions. In React, they are particularly useful because they do not bind their own, and preventing issues in callbacks.
Here is the comparison of react and react native:
Lists in React are created using the map() function to iterate over an array of data, generating a set of elements. Each element in the list should have a unique key prop to help React identify and manage updates efficiently.
Keys are essential for identifying which items in a list have changed, been added, or removed. They help React optimize rendering by allowing it to re-render only the changed components rather than the entire list.
Synthetic events are React's cross-browser wrapper for native events. They provide a consistent API and help in normalizing event properties across different browsers, ensuring compatibility.
npx create-react-app my-app.You create an event in React by defining an event handler function and attaching it to an element using JSX. For example:
<button onClick={this.handleClick}>Click me</button>
Controlled components depend on the state to manage their values, meaning that form inputs are controlled by React's state. This approach provides better data flow, validation, and easier management of form state. While uncontrolled components store their values in the DOM, allowing the input elements to maintain their state.
function Counter() {
const [count, setCount] = useState(0);
return (
<div>
<p>{count}</p>
<button onClick={() => setCount(count + 1)}>Increment</button>
<button onClick={() => setCount(count - 1)}>Decrement</button>
</div>
);
}
Props are read-only data passed from parent components to child components, allowing for data flow and communication. While the state is mutable and managed within a component. It is used to track local component data that can change over time, triggering re-renders when updated.
function TodoApp() {
const [todos, setTodos] = useState([]);
const [input, setInput] = useState("");
const addTodo = () => {
setTodos([...todos, input]);
setInput("");
};
return (
<div>
<input value={input} onChange={(e) => setInput(e.target.value)} />
<button onClick={addTodo}>Add</button>
<ul>
{todos.map((todo, index) => (
<li key={index}>{todo}</li>
))}
</ul>
</div>
);
}
Authentication can be managed using context or state management libraries such as Redux to store user data. Higher-order components are used to wrap protected routes, authenticating before rendering the components. Using JWT tokens in API requests is also standard procedure.
Static routing refers to predefined routes that do not change, while dynamic routing allows routes to be defined at runtime based on data. Dynamic routing can be achieved using route parameters and can change based on application state or API responses.
React's synthetic event system is a cross-browser wrapper around the browser's native event system. It normalizes events so that they have consistent properties across different browsers. Synthetic events are pooled for performance, meaning that their properties are reused, which is why you cannot access event properties asynchronously without calling event.persist().
function FetchData() {
const [data, setData] = useState([]);
useEffect(() => {
fetch("https://jsonplaceholder.typicode.com/posts")
.then(response => response.json())
.then(data => setData(data));
}, []);
return (
<ul>
{data.map(item => (
<li key={item.id}>{item.title}</li>
))}
</ul>
);
}
Custom hooks are JavaScript functions that use React hooks and encapsulate reusable logic. They can take arguments and return values. You create a custom hook by defining a function that starts with "use" and inside it, you can use other hooks as needed. For example, function useFetch(url) { ... }.
The following are some of the best tips that can ensure you excel in your react coding interview questions:
React coding interviews can be challenging, but thorough preparation and practice can significantly increase your chances of success. Focus on understanding both basic and advanced concepts, and don't hesitate to build projects that highlight your skills.