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Interview Question (React) ‐ Part 2

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Anurag Mishra edited this page Jun 7, 2024 · 3 revisions

31. What are the essential components required to design a shopping cart for an ecommerce website where products are displayed with an "Add to Cart" button, and on clicking the button, the cart gets updated?

Essential components for a shopping cart in React might include:

  • ProductList: Component to display the list of products with their details and an "Add to Cart" button.
  • Cart: Component to display the items added to the cart, their quantity, and total price.
  • CartItem: Component to display individual items in the cart with options to adjust quantity or remove.
  • CartButton: Component to display the cart icon and show the number of items in the cart.
  • ShoppingCart: Component to manage the state of the cart and handle actions like adding/removing items and updating quantities.

32. What is the advantage of choosing props over states?

Props are used to pass data from parent to child components, while state is used to manage internal component data. Choosing props over state promotes a more predictable flow of data in your application and improves component reusability. Props are immutable and can help maintain the purity of your components, making them easier to reason about and test.

33. Can you provide a detailed explanation of how to submit a form using react-redux form and display success/error messages based on the response?

To submit a form using react-redux-form, you would typically dispatch an action when the form is submitted. This action would trigger an API call to submit the form data to the server. Based on the response from the server, you can dispatch additional actions to update the Redux store with success or error messages. These messages can then be displayed in your React components based on their state in the Redux store.

34. How would you redirect to a route in React?

In React, you can redirect to a route using the Redirect component from React Router or by using the history object provided by React Router. For example:

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

// Inside your component render method
render() {
  return <Redirect to="/new-route" />;
}

35. How can we directly access DOM in react?

Directly accessing the DOM in React is discouraged because React manages the DOM itself. However, if you need to access the DOM for some reason, you can use refs. Refs allow you to reference a DOM element directly within a React component. You can create a ref using the React.createRef() method and then attach it to a DOM element using the ref attribute.

36. Which build tool do you use to create a production-ready build for React applications, and what steps do you take to optimize the build size and ensure minimal file size for efficient production deployment?

Common build tools for creating production-ready builds for React applications include Webpack and Create React App. To optimize build size, you can:

  • Use code splitting to split your code into smaller chunks.
  • Minify and compress your JavaScript and CSS files.
  • Remove unused code and dependencies.
  • Enable gzip compression on your server to further reduce file size.
  • Utilize tree shaking to remove unused code from your bundle. Certainly! Let's continue with the remaining interview questions:

37. What is Context API?

Context API is a feature introduced in React 16.3 to provide a way to pass data through the component tree without having to pass props manually at every level. It allows you to share values like themes, language preferences, or authentication status across components without the need for prop drilling. Context consists of two main parts: the Provider component, which provides the context value, and the Consumer component, which consumes the context value within nested components.

38. Explain React Hooks.

React Hooks are functions that let you use state and other React features in functional components. They allow you to use state and other React features without writing a class. Some commonly used hooks include useState for managing state, useEffect for handling side effects, useContext for accessing context, and more. Hooks provide a simpler and more functional approach to managing state and side effects in React applications.

39. Define mapStateToProps and mapDispatchToProps.

mapStateToProps is a function used to specify which parts of the Redux store's state should be passed to a connected component as props. It takes the entire Redux store state as an argument and returns an object containing the props to be passed to the component. mapDispatchToProps is a function used to specify which action creators should be available to a connected component as props. It takes the dispatch function as an argument and returns an object containing the action creators to be passed to the component.

40. What is a store?

In Redux, a store is an object that holds the entire state tree of your application. The state is read-only, and the only way to change it is by dispatching actions. The store also includes methods for subscribing to changes in the state and dispatching actions. It serves as the single source of truth for the state of your application.

41. What is the purpose of the Switch component in React Router, and how is it used for declarative routing in a React application?

The Switch component in React Router is used to render only the first <Route> or <Redirect> that matches the current location. This is useful for declarative routing because it allows you to specify multiple routes without worrying about rendering multiple components. The Switch component iterates over its children and renders the first one that matches the current URL path, ignoring all others.

42. What is the process for installing and setting up React Router in a React application, and what are the recommended steps to ensure proper integration and usage of the router library in the project?

To install React Router, you can use npm or yarn:

npm install react-router-dom

or

yarn add react-router-dom

Once installed, you can set up routing in your application by wrapping your components with BrowserRouter or HashRouter and defining routes using the Route component. It's also important to set up a catch-all route using the Switch component to handle 404 errors. Additionally, you can use other components provided by React Router like Link for navigation and Redirect for programmatic redirection.

43. How does routing contribute to the development of single-page applications in ReactJS, and what benefits does it offer in terms of organizing the user interface and improving the overall user experience?

Routing in ReactJS enables the creation of single-page applications (SPAs) where the entire application is contained within a single HTML page. This allows for faster navigation between views since only the content that changes needs to be fetched and rendered. Routing also helps in organizing the user interface by defining different views for different routes, making the application structure more modular and maintainable. Additionally, routing improves the overall user experience by providing a seamless navigation experience similar to traditional multi-page applications.

44. How do you validate props in a React component?

You can validate props in a React component using the propTypes property or the prop-types library. propTypes is a built-in feature of React that allows you to specify the expected data types of props passed to a component. For example:

import PropTypes from 'prop-types';

function MyComponent(props) {
  // Component logic

  return <div>{props.message}</div>;
}

MyComponent.propTypes = {
  message: PropTypes.string.isRequired
};

This will throw a warning in development mode if the message prop is not a string or is missing.

45. What are the various data types that can be specified using the propTypes library in a React component, and how can you use them to define the expected data types of the props passed to the component?

The propTypes library allows you to specify various data types for props, including string, number, boolean, object, array, func, symbol, node, element, and custom data types. You can use them to define the expected data types of props by assigning them to the corresponding prop keys in the component's propTypes property. Additionally, you can specify that a prop is required using the .isRequired modifier.

46. In React, what are the parameters of the map() function and how is it used to manipulate arrays?

The map() function in React takes a callback function as its parameter, which is called for each element in the array. This callback function can take up to three arguments: currentValue, index, and array. It returns a new array with the results of calling the provided function on every element in the calling array. The map() function is commonly used to iterate over an array, perform some operation on each element, and return a new array with the modified elements.

47. What is the reason for requiring a "key" when using the map() function in React and how does it help in rendering arrays efficiently?

In React, when rendering a list of elements using the map() function, each element in the array must have a unique key prop. This helps React identify which items have changed, been added, or been removed. Without keys, React may re-render every item in the list on every state change, leading to poor performance. Keys help React optimize the rendering process by efficiently updating and reordering elements as needed.

48. What are combined reducers in Redux?

Combined reducers in Redux are used to manage multiple slices of state in a Redux store. They allow you to break down the root reducer into smaller, more manageable reducers, each responsible for managing a specific slice of state. The combineReducers function provided by Redux takes an object as its argument, where each key-value pair corresponds to a slice of state and its corresponding reducer function. When an action is dispatched, each reducer is called with the slice of state it manages, and the combined state is updated accordingly.

49. Can you provide a detailed explanation of what Redux is, its purpose, and walk through the complete flow of Redux in a React application?

Redux is a predictable state container for JavaScript applications, commonly used with React for managing application state. Its purpose is to centralize application state in a single store, making it easier to manage and reason about. The flow of Redux in a React application typically involves the following steps:

  • Define actions: Plain JavaScript objects describing state changes.
  • Create reducers: Functions that specify how the state changes in response to actions.
  • Create a store: A single source of truth for the application state, initialized with the root reducer.
  • Connect components: Use the connect function from React Redux to connect components to the Redux store.
  • Dispatch actions: Call the dispatch function with actions to trigger state changes.
  • Update components: React components connected to the Redux store receive updated props when the state changes, triggering re-renders.

50. What are the differences between the bind(), call(), and apply() methods in JavaScript and how are they used to manipulate the ‘this’ keyword and pass arguments to functions?

  • bind(): Creates a new function with a specified this value and optional arguments. It does not invoke the function immediately but returns a new function that, when called, will have the specified this value. Example: func.bind(thisArg, arg1, arg2).

  • call(): Invokes a function with a specified this value and arguments passed individually. It immediately invokes the function. Example: func.call(thisArg, arg1, arg2).

  • apply(): Similar to call(), but arguments are passed as an array. It immediately invokes the function. Example: func.apply(thisArg, [arg1, arg2]).

These methods are used to control the context (this keyword) of a function and pass arguments to it explicitly.

51. In React, what are inline functions and how are they used to handle events and pass data between components?

Inline functions in React are functions defined directly within the JSX code of a component. They are commonly used to handle events, such as onClick or onChange, and pass data between components. Inline functions allow you to execute code and pass parameters directly when an event occurs without needing to define separate event handler functions. For example:

<button onClick={() => handleClick(id)}>Click Me</button>

In this example, an inline function is used to call the handleClick function with the id parameter when the button is clicked.

52. What are the various approaches for writing a click event handler in React, and how do they differ in terms of syntax and functionality?

There are multiple approaches for writing click event handlers in React:

  • Inline arrow functions: Directly define a function within the JSX code of the component. Example: <button onClick={() => handleClick()}>Click Me</button>.

  • Binding in the constructor: Bind the event handler function to the component's this context in the constructor. Example: this.handleClick = this.handleClick.bind(this); and <button onClick={this.handleClick}>Click Me</button>.

  • Class property arrow functions: Define the event handler function as a class property using an arrow function. Example: handleClick = () => { // handle click logic } and <button onClick={this.handleClick}>Click Me</button>.

  • Using bind(): Bind the event handler function in the JSX code directly. Example: <button onClick={this.handleClick.bind(this)}>Click Me</button>.

Each approach has its own syntax and functionality, but they all achieve the same result of handling click events in React components.

53. What are the distinctions between Bootstrap and Material UI, and what are the advantages of using both of them in web development projects?

Bootstrap and Material UI are popular front-end frameworks for building user interfaces, but they have some distinctions:

  • Design philosophy: Bootstrap follows a flat design with a focus on simplicity and consistency, while Material UI is based on Google's Material Design principles, emphasizing depth, motion, and material properties.

  • Component styles: Bootstrap provides pre-styled UI components like buttons, forms, and cards, while Material UI offers components styled according to the Material Design guidelines.

  • Customization: Bootstrap is highly customizable with extensive documentation and theming options, while Material UI offers theming support but may require more effort for customization.

Using both frameworks in web development projects can offer advantages such as access to a wide range of pre-designed components, consistent styling across applications, and support for responsive design out of the box.

54. What are the useState, useEffect, and useContext hooks in React, and how are they used to manage state, perform side effects, and handle global data respectively?

  • useState: A hook used to add state to functional components. It returns a stateful value and a function to update it, allowing functional components to manage state without using class components.

  • useEffect: A hook used to perform side effects in functional components. It allows you to perform operations like data fetching, subscriptions, or manual DOM manipulation after React has updated the DOM.

  • useContext: A hook used to access context in functional components. It allows you to consume context values created by a Provider component higher up in the component tree, enabling global state management and sharing of data between components without prop drilling.

55. What is meant by embedding in software development, and how is it related to the version control system Git?

In software development, embedding refers to the practice of including external resources or dependencies within a project's source code or repository. This can include libraries, frameworks, images, or other assets. Embedding resources in a project ensures that it remains self-contained and can be easily distributed and deployed without external dependencies. In the context of version control systems like Git, embedding involves committing external resources directly to the repository rather than relying on external references or dependencies. While embedding can simplify project setup and deployment, it may also increase repository size and make version control more complex.

56. What are the assign() and reduce() functions in JavaScript, and how are they used to manipulate arrays and objects?

  • Object.assign(): A method used to copy the values of all enumerable own properties from one or more source objects to a target object. It returns the modified target object. Example: const newObj = Object.assign({}, obj1, obj2);.

  • Array.reduce(): A method used to reduce an array to a single value by applying a function to each element of the array, accumulating the result. It takes an accumulator function and an initial value as arguments. Example: const sum = array.reduce((acc, curr) => acc + curr, 0);.

These functions are commonly used to manipulate arrays and objects in JavaScript by combining or transforming their values.

57. Can you explain the concept of hoisting in JavaScript, and provide an example of how it affects variable and function declarations?

Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their containing scope during the compilation phase, before the code is executed. However, only the declarations are hoisted, not the initializations. For example:

console.log(x); // undefined
var x = 10;

In this example, even though the variable x is accessed before it is declared, it doesn't result in a ReferenceError. This is because variable declarations (not initializations) are hoisted to the top of the scope.

58. Could you provide a program example of an uncontrolled component in React, and elaborate on the concept of uncontrolled components in terms of state management, as well as how they differ from controlled components?

Uncontrolled components in React are components that manage their own state internally using refs, rather than relying on React state. Here's an example of an uncontrolled component:

import React, { useRef } from 'react';

function UncontrolledComponent() {
  const inputRef ```jsx
= useRef(null);

  const handleSubmit = () => {
    console.log(inputRef.current.value);
  };

  return (
    <div>
      <input type="text" ref={inputRef} />
      <button onClick={handleSubmit}>Submit</button>
    </div>
  );
}

export default UncontrolledComponent;

In this example, the inputRef is created using the useRef hook to create a reference to the input element. When the user types into the input field and clicks the "Submit" button, the handleSubmit function is called, which accesses the current value of the input field using inputRef.current.value.

Uncontrolled components differ from controlled components in that controlled components manage their state using React state, where the component's state is stored in the component's state variables and updated using setState. In contrast, uncontrolled components manage their state internally using DOM refs, bypassing React's state management mechanism.

59. Explain the concept of debouncing and throttling in JavaScript, and provide examples of how they can be implemented to improve performance in web applications.

  • Debouncing: Debouncing is a technique used to limit the rate at which a function is invoked. It ensures that a function is not called repeatedly in a short period of time, but rather only after a certain amount of time has passed since the last invocation. This can be useful for scenarios like handling user input in search boxes, where you only want to perform the search after the user has stopped typing for a brief moment.
function debounce(func, delay) {
  let timeoutId;
  return function(...args) {
    clearTimeout(timeoutId);
    timeoutId = setTimeout(() => {
      func.apply(this, args);
    }, delay);
  };
}

const debouncedSearch = debounce(searchFunction, 300);
input.addEventListener('input', debouncedSearch);
  • Throttling: Throttling is a technique used to ensure that a function is not called more than once in a specified time interval. It limits the execution rate of the function by delaying subsequent invocations until the specified interval has elapsed. Throttling is commonly used in scenarios like handling scroll events or resizing windows, where you want to limit the frequency of function calls to improve performance.
function throttle(func, limit) {
  let inThrottle;
  return function(...args) {
    if (!inThrottle) {
      func.apply(this, args);
      inThrottle = true;
      setTimeout(() => {
        inThrottle = false;
      }, limit);
    }
  };
}

const throttledScroll = throttle(scrollHandler, 300);
window.addEventListener('scroll', throttledScroll);

Both debouncing and throttling can improve the performance of web applications by reducing the frequency of function calls in scenarios where rapid invocations are not necessary.

60. Explain the concept of closures in JavaScript, and provide an example of how they can be used to encapsulate state and create private variables and functions.

Closures are a fundamental concept in JavaScript that allows inner functions to access variables from their outer lexical scope even after the outer function has finished executing. This means that the inner function retains access to the variables and parameters of the outer function, even when the outer function's execution context is no longer active.

function outerFunction() {
  let count = 0;

  function innerFunction() {
    count++;
    console.log(count);
  }

  return innerFunction;
}

const incrementCounter = outerFunction();
incrementCounter(); // Output: 1
incrementCounter(); // Output: 2

In this example, the innerFunction has access to the count variable defined in the outerFunction, even though outerFunction has already finished executing. This creates a closure around the count variable, allowing the inner function to maintain its state between invocations.

Closures can be used to encapsulate state and create private variables and functions, making them accessible only within the scope of the outer function. This is useful for creating modules, implementing data hiding, and preventing variable pollution in JavaScript code.

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