Wipro React js Interview Questions and Answers

As you prepare for your Wipro React.js interview, this blog serves as your comprehensive guide, arming you with the knowledge and confidence to navigate the technical challenges with ease. Use these questions and answers as a stepping stone to not only meet but exceed Wipro's expectations, securing your place as a valuable asset in their esteemed team of technology professionals. Good luck on your journey to mastering the Wipro React.js interview

Q1. What are Closures, Hoiting and Semantic elements with examples?

Ans: Closures, hoisting, and semantic elements are different concepts in programming and web development. Let me briefly explain each of them:

1. Closures: A closure is a feature in programming languages that allows functions to remember the variables in their lexical scope even when the function is executed outside that scope. In simpler terms, a closure allows a function to access variables from its outer (enclosing) function even after that outer function has finished executing.

Example in JavaScript:

function outerFunction() {
  let outerVariable = 10;

  function innerFunction() {
    console.log(outerVariable);
  }

  return innerFunction;
}

const closureExample = outerFunction();
closureExample(); // Outputs 10

2. Hoisting: Hoisting is a behavior in JavaScript where variable and function declarations are moved to the top of their containing scope during the compilation phase. This allows you to use variables and functions before they are declared in the code.

Example in JavaScript:

console.log(x); // Outputs 'undefined'
var x = 5;
console.log(x); // Outputs 5

3. Semantic Elements: Semantic elements in HTML are tags that carry meaning about the structure and content of a web page. They provide a more descriptive and meaningful way to structure a document, making it easier for both developers and browsers to understand the content.
Examples of semantic elements include <header>, <footer>, <nav>, <article>, <section>, <aside>, <figure>, <figcaption>, etc.

<header>
  <h1>My Website</h1>
</header>

<nav>
  <ul>
    <li><a href="#home">Home</a></li>
    <li><a href="#about">About</a></li>
    <li><a href="#contact">Contact</a></li>
  </ul>
</nav>

<section>
  <article>
    <h2>Article Title</h2>
    <p>Article content goes here...</p>
  </article>

  <article>
    <h2>Another Article Title</h2>
    <p>More content...</p>
  </article>
</section>

<footer>
  <p>&copy; 2023 My Website</p>
</footer>

 

Q2. What is Promise?

Ans: A Promise is an object in JavaScript that represents the eventual completion or failure of an asynchronous operation and its resulting value. It is a part of the ECMAScript 6 (ES6) standard and provides a way to work with asynchronous code in a more structured and manageable manner.

A Promise can be in one of three states:

1. Pending: The initial state; the promise is neither fulfilled nor rejected.
2. Fulfilled: The operation completed successfully, and the promise has a resulting value.
3. Rejected: The operation failed, and the promise has a reason for the failure.

A basic syntax for creating a Promise looks like this:

const myPromise = new Promise((resolve, reject) => {

  // Asynchronous operation or task

  // If successful, call resolve(value)

  // If an error occurs, call reject(reason)

});

Here's a simple example to illustrate the concept:

const fetchData = () => {
  return new Promise((resolve, reject) => {
    // Simulating an asynchronous operation, like fetching data from an API
    setTimeout(() => {
      const data = { name: 'John', age: 30 };
      // Simulating a successful operation
      resolve(data);
      // Simulating an error
      // reject(new Error('Failed to fetch data'));
    }, 2000);
  });
};

// Using the Promise
fetchData()
  .then(result => {
    console.log('Data:', result);
  })
  .catch(error => {
    console.error('Error:', error.message);
  });

In this example, fetchData returns a Promise that simulates fetching data asynchronously. The .then() method is used to handle the successful resolution of the Promise, and the .catch() method is used to handle any errors that may occur during the asynchronous operation.

Promises are especially useful when dealing with asynchronous tasks, such as fetching data from a server, reading a file, or making an HTTP request, and they provide a cleaner alternative to callback-based approaches. Promises also allow chaining, making it easier to compose asynchronous operations sequentially.

 

Q3. What is State and Stateless?

Ans: In the context of computer science, programming, and web development, "state" and "stateless" refer to the concept of whether a system or component maintains information about its current condition or not.

1. State:

• Definition: State refers to the current condition or mode of a system, object, or application. It represents the values of all relevant variables and the configuration of the system at a given point in time.
• Example: In a web application, the state could include user input, the current page, whether a user is logged in, etc. For instance, if you're filling out a form online and you navigate away, the application might remember what you've entered so far, indicating that it's maintaining a certain state.

2. Stateless:

• Definition: A system or component is stateless if it does not store any information about its current state between requests. Each request from a client to a stateless system is independent and contains all the information needed for the server to fulfill that request.
• Example: The Hypertext Transfer Protocol (HTTP) is a stateless protocol. Each HTTP request from a client to a server is independent, and the server doesn't retain any information about previous requests from the same client. Web applications often use techniques like cookies or sessions to simulate statefulness.
• Statelessness in Web Development: In web development, statelessness is often associated with stateless protocols like HTTP. Stateless web applications are designed to handle each request independently, and they don't retain information about the user's interactions between requests. Statelessness simplifies scaling and makes systems more robust, but it also requires additional mechanisms (such as cookies or tokens) to maintain user-related state.

It's worth noting that the term "stateless" can have different meanings in various contexts, so the specific interpretation may depend on the technology or system being discussed.

 

Q4. What are Chaining methods?

Ans: Chaining methods is a programming technique where multiple methods are called on an object or a result of a function in a single, sequential line. This is often used to make code more concise and readable, especially when working with functions or methods that return the modified object or a new result. This is a common pattern in many programming languages, including JavaScript.

Here's an example of method chaining with React components using JSX:

import React from 'react';

class MyComponent extends React.Component {
  handleClick = () => {
    // Handle click logic
  };

  render() {
    return (
      <div>
        <h1 onClick={this.handleClick}>Click me!</h1>
        <p>This is a React component.</p>
      </div>
    );
  }
}
export default MyComponent;

In this example, the onClick event handler is a method that is chained to the h1 element in JSX. This is a common pattern in React to attach event handlers to elements.

If you have a more specific question or if you're referring to a different type of method chaining in the context of React, please provide more details so I can assist you better.

 

Q5. Why are react hooks useful?

Ans: React Hooks are useful for several reasons, and they were introduced in React 16.8 to address some limitations and complexities associated with class components. Here are some key benefits and reasons why React Hooks are valuable:

1. Simplified Component Logic:

• With class components, managing stateful logic or side effects often required the use of lifecycle methods, which could make the code more complex and harder to understand. Hooks, such as useState and useEffect, allow you to handle state and side effects more simply and directly within functional components.

2. Code Reusability:

• Hooks promote the reuse of stateful logic across components. Custom hooks enable developers to extract and share common logic, making it easier to manage and maintain the codebase.

3. Functional Components with State:

• Prior to hooks, functional components were stateless and couldn't manage their own state. With hooks like useState, functional components can now manage local state, reducing the need for class components in many cases.

4. No Need for Class Components:

• Hooks provide an alternative to class components, making it possible to write entire applications using only functional components. This simplifies the mental model for developers and reduces the need to understand and use class-related concepts.

5. Improved Code Readability:

• Hooks allow you to organize and separate concerns more clearly. For example, the useState hook declares state variables at the top level of the component, and the useEffect hook groups side effects together. This can lead to more readable and maintainable code.

6. Avoidance of this Keyword:

• Class components use the this keyword, which can be confusing and lead to unexpected behavior. Functional components using hooks don't rely on this, which can simplify the code and reduce potential issues related to binding.

7. Easier Testing:

• Because hooks encourage functional programming practices, components built with hooks are often easier to test. Logic can be extracted into custom hooks, and these hooks can be tested independently of the components.

8. Better Support for Future React Features:

• Hooks are a part of the React core API, and they are expected to be the primary way of handling stateful logic in React. As new features and optimizations are introduced, they are likely to be built around the hook API.

In summary, React Hooks provide a more straightforward and functional way to manage state and side effects in React components, promoting code simplicity, reusability, and improved developer experience. They have become a standard and recommended practice for writing React components.

 

Q6. What are HOC components?

Ans: HOC stands for Higher-Order Component in React. A Higher-Order Component is a function that takes a component and returns a new component with additional props and behavior. It's a pattern used for code reuse, especially when you want to share component logic among multiple components.

Here's a simple example to illustrate the concept of a Higher-Order Component:

import React from 'react';

// Higher-Order Component
const withLogging = (WrappedComponent) => {
  class WithLogging extends React.Component {
    componentDidMount() {
      console.log(`Component ${WrappedComponent.name} is mounted.`);
    }

    componentWillUnmount() {
      console.log(`Component ${WrappedComponent.name} is unmounted.`);
    }

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

  return WithLogging;
};

// Example usage of the Higher-Order Component
class MyComponent extends React.Component {
  render() {
    return <div>My Component</div>;
  }
}

const MyComponentWithLogging = withLogging(MyComponent);

// Now, MyComponentWithLogging has the added logging behavior

In this example, withLogging is a Higher-Order Component that takes a component (WrappedComponent) and returns a new component (WithLogging). The new component includes lifecycle methods for logging when the component is mounted and unmounted.

The usage of the Higher-Order Component involves wrapping the original component (MyComponent) with the HOC (withLogging). The resulting component (MyComponentWithLogging) has the added behavior from the HOC.

Higher-Order Components are powerful for code reuse and abstraction. They allow you to encapsulate common logic and features and apply them to multiple components without duplicating code. Keep in mind that with the introduction of Hooks in React, many patterns that were traditionally achieved using HOCs can now be accomplished using custom hooks and functional components.

 

Q7. What are fragments in react js?

Ans: In React, a fragment is a lightweight syntax for grouping multiple elements without introducing an additional parent container in the DOM. Fragments were introduced in React 16.2 to address the issue of having unnecessary wrapper elements when you wanted to return multiple elements from a component.

Instead of using a container element like a <div> to wrap multiple elements, you can use a fragment, which doesn't create an extra node in the DOM. Fragments can be expressed using either the long syntax or the shorthand syntax.

Long Syntax:

import React from 'react';

class MyComponent extends React.Component {
  render() {
    return (
      <React.Fragment>
        <p>Paragraph 1</p>
        <p>Paragraph 2</p>
      </React.Fragment>
    );
  }
}

Shorthand Syntax:

import React from 'react';

class MyComponent extends React.Component {
  render() {
    return (
      <>
        <p>Paragraph 1</p>
        <p>Paragraph 2</p>
      </>
    );
  }
}

Both syntaxes achieve the same result: they group multiple elements without adding an extra DOM node. Fragments are particularly useful in situations where a container element is undesirable or when you want to avoid affecting the layout or styling.

Prior to the introduction of fragments, developers often used unnecessary <div> or other container elements solely for the purpose of satisfying the requirement that a component must return a single root element. Fragments provide a cleaner and more concise way to achieve the same goal without introducing unnecessary elements to the DOM.

 

Q8. What is Redux?

Ans: Redux is a state management library for JavaScript applications, commonly used with React for building user interfaces. It provides a predictable state container, allowing you to manage the state of your application in a centralized manner. Redux is particularly useful in large and complex applications where managing the state becomes challenging.

Core Concepts of Redux:

1. Store:

• The store is the central repository of the state in a Redux application. It holds the complete state tree of the application. You can think of it as a single JavaScript object that represents the entire state.

2. Actions:

• Actions are plain JavaScript objects that describe changes in the application state. They are the only source of information for the store. Actions typically have a type property indicating the type of action and may include additional data (payload).

3. Reducers:

• Reducers are pure functions responsible for specifying how the state changes in response to actions. They take the current state and an action as arguments and return a new state. Reducers should not modify the existing state but rather return a new copy.

4. Dispatch:

• The store has a dispatch method that is used to dispatch actions to the reducers. When an action is dispatched, the store invokes the appropriate reducer to update the state based on the action.

5. Selectors:

• Selectors are functions that extract specific pieces of data from the state. They help in isolating the components from the structure of the state and make it easier to access the required data.

Basic Redux Workflow:

1. Action is Dispatched:

• An action is dispatched using store.dispatch(action).

2. Reducer Responds:

• The corresponding reducer is called with the current state and the action. The reducer returns a new state based on the action.

3. State is Updated:

• The store's state is updated with the new state returned by the reducer.

4. Components Re-render:

• Connected React components that are subscribed to the store are notified of the state change and re-render with the updated data.

Example:

Here's a simple example of a Redux setup:

// Actions
const increment = () => ({ type: 'INCREMENT' });
const decrement = () => ({ type: 'DECREMENT' });

// Reducer
const counterReducer = (state = 0, action) => {
  switch (action.type) {
    case 'INCREMENT':
      return state + 1;
    case 'DECREMENT':
      return state - 1;
    default:
      return state;
  }
};

// Store
const { createStore } = require('redux');
const store = createStore(counterReducer);

// Dispatching actions
store.dispatch(increment());
console.log(store.getState()); // Output: 1

store.dispatch(decrement());
console.log(store.getState()); // Output: 0

In this example, actions (increment and decrement) are dispatched to the store, and the reducer (counterReducer) responds by updating the state based on the action type. The store keeps track of the state, and components can subscribe to changes in the state using the store.subscribe method. React components can also connect to the Redux store using the react-redux library.