ReactJS Interview Questions Part-4

How to dispatch an action on load in ReactJS?

To dispatch an action on load in ReactJS, you can use the useEffect hook provided by React. Within the useEffect hook, you can dispatch the desired action using Redux or any other state management library you are using.

Here’s an example of how you can dispatch an action on component load in ReactJS:

import React, { useEffect } from 'react';
import { useDispatch } from 'react-redux';
import { fetchInitialData } from '../actions'; // Replace with your own actionfunction MyComponent() {
  const dispatch = useDispatch();
  useEffect(() => {
    dispatch(fetchInitialData()); // Dispatch your action here
  }, []);  // Rest of your component code
  return (
    // JSX for your component
export default MyComponent;

In this example, we import the useEffect hook and the useDispatch hook from React and Redux respectively. Then, we define our functional component MyComponent

Inside MyComponent, we use the useEffect hook to execute the dispatching of the action.The second argument of the useEffect hook is an empty dependency array [], which means the effect will only run once on component mount. 

This ensures that the action is dispatched only when the component is loaded.You should replace fetchInitialData with your own action that you want to dispatch on component load.

Remember to connect your component to the Redux store using the connect higher-order component or the useSelector hook if you’re using React Redux Hooks.I hope this helps! Let me know if you have any further questions.

Why do you not required to use inheritance in ReactJS?

In ReactJS, a JavaScript library for building user interfaces, the concept of inheritance is not required for several reasons. 

One of the main reasons is that React follows a component-based architecture, where reusable components are the building blocks of the UI. Components in React are designed to be self-contained and independent entities that encapsulate their own state and behavior. This approach promotes reusability and modularity by allowing components to be composed together to create complex UIs.

Instead of relying on inheritance, React uses a mechanism called “composition” to compose components. Composition refers to the ability to combine smaller components together to form larger ones. This can be achieved using props, which allow you to pass data and functions between components. By passing data and functionality through props, components can interact with each other, exchange information, and achieve the desired behavior.

Another reason why inheritance is not required in React is that it promotes a more declarative approach to building UIs. React encourages you to describe how your UI should look at any given point in time, rather than imperatively manipulating its state. This declarative style allows React to efficiently update and render components when their state changes, resulting in better performance.

Overall, React’s focus on composition, reusability, and declarative programming makes inheritance unnecessary for creating complex UIs. Instead, React provides a flexible, efficient, and modular way of building user interfaces by leveraging components and composition.

What is React Dev Tools?

React Dev Tools is a browser extension that is used as a debugging tool specifically for React applications. It is developed by the React team and is available for popular browsers such as Chrome, Firefox, and Edge.

React Dev Tools allows developers to inspect and manipulate the component hierarchy and state of their React application, making it easier to understand and debug complex UI components. It provides a user-friendly interface that shows the component tree, props, and state values for each component rendered on a webpage.

With React Dev Tools, developers can quickly identify which components are responsible for rendering certain parts of the UI, inspect and modify their props and state, monitor component performance, and even simulate user interactions. This tool greatly aids in the development and debugging process, making it an essential tool for React developers.

In addition to inspecting and manipulating components, React Dev Tools also provides useful features such as highlighting updates to components, profiling performance, and analyzing the virtual DOM. These features help developers optimize their React applications for better performance and user experience.

Overall, React Dev Tools is a powerful tool that enhances the developer experience when working with React applications, allowing for efficient debugging, performance analysis, and optimization.

What is the proper way to access Redux store in in ReactJS?

In ReactJS, the proper way to access the Redux store is by using the connect function provided by the react-redux library. This allows you to connect your component to the store and access the state and dispatch actions.

Here’s a step-by-step guide:

1. Install the necessary dependencies:

npm install react-redux redux

2. Import the required functions from the react-redux library:

import { connect } from 'react-redux';   

3. Define your component as usual, and create a function that maps the state from the Redux store to your component’s props:

  const MyComponent = ({ myState }) => {
     // ...
   const mapStateToProps = (state) => {
     return {
       myState: state.myReducer.myState,

4. Use the connect function to connect your component to the Redux store. Pass in the mapStateToProps function as the first argument:

export default connect(mapStateToProps)(MyComponent);   

5. Now, your component will have access to the state from the Redux store as a prop. You can use it like this:

 const MyComponent = ({ myState }) => {
     return {myState};

By using the connect function, your component will automatically subscribe to updates from the Redux store and re-render when the state changes. 

Additionally, you can dispatch actions by using the dispatch function, which will also be available as a prop in your component. I hope this helps! Let me know if you have any further questions.

What is Redux Form in ReactJS?

Redux Form is a library that provides a convenient way to manage form state in React applications while utilizing Redux. It is a layer of abstraction built on top of Redux that simplifies the process of handling form submission, validation, and state management.

When using Redux Form, the form state is kept in the Redux store, allowing for easy access and management of form data across different components. It follows the principles of unidirectional data flow and immutability provided by Redux, which helps to maintain a predictable state throughout the application.

With Redux Form, you can define your form fields, validation rules, and handling of form submission using a declarative syntax. It provides a set of components and actions that handle common form functionality, such as input fields, checkboxes, radio buttons, dropdowns, and more. These components are connected to the Redux store, allowing them to automatically update the form state when user input changes.

One of the key features of Redux Form is its support for form validation. You can define validation functions for each field and easily display error messages based on the validation results. Redux Form also provides options for asynchronous validation, enabling you to perform server-side validation or other async operations while the user interacts with the form.

Another powerful feature of Redux Form is its ability to handle form submission and manage the submission status. It provides actions and lifecycle events that allow you to track whether the form is being submitted, successfully submitted, or encountered an error during submission. This gives you fine-grained control over the form submission process and makes it easier to handle different scenarios.

Overall, Redux Form simplifies the process of managing form state in React applications, providing a scalable and maintainable solution for handling complex forms. It saves development time by abstracting away the low-level details of form management and integrating seamlessly with Redux and React.

Why do not you need error boundaries for event handlers in ReactJS?

In ReactJS, error boundaries are not needed for event handlers because event handling in React follows a different flow compared to component rendering. 

When an error occurs inside an event handler, it is considered a JavaScript error rather than a React component error. During event handling, React does not actually render any components, but instead it relies on the browser’s built-in event system.

JavaScript errors during event handling are typically caught globally by the browser, and can be handled using traditional JavaScript error handling techniques like try-catch blocks or window.onerror event handlers. React does not intercept these errors, as it assumes that you will handle them appropriately outside of its component hierarchy.

That being said, if an event handler triggers a state update or a component re-render, and an error occurs within that component, then React’s error boundary mechanism will come into play. In these cases, an error boundary component can be used to catch and handle errors occurring during rendering or lifecycle methods within React components.

So, in summary, React does not provide special error handling mechanisms for event handlers because they are outside the scope of React’s rendering pipeline, and the responsibility for handling JavaScript errors in event handlers lies with the browser’s native error handling mechanisms.

What is the significance of keys in ReactJS?

In ReactJS, keys play a significant role when rendering lists of components. They help React identify which items have changed, been added, or been removed in a list, allowing it to efficiently update the user interface.

When you render a list of items in React, you typically use a map or similar function to create an array of components. Each rendered component needs a unique “key” prop assigned to it. This key should be a stable identifier for each item in the list. Usually, you can use a unique ID associated with each item, but any other distinguishing attribute would work as well.

The key allows React to optimize the rendering process by minimizing re-renders and reconciling differences between the previous and updated lists. When React detects a key change, it knows that a new item has been added or an existing one has been removed, triggering the appropriate actions without affecting the entire list.

Without keys, React may resort to using the index of each item as a default key. While this works for simple cases, it can lead to performance issues and unexpected behavior when the list order changes or items are added/removed dynamically. Therefore, it’s generally recommended to provide explicit and stable keys for your list items.

By using keys correctly, you can improve the performance of your React applications, eliminate unnecessary re-renders, and ensure that state management and event handling remain consistent across component updates.

How to access current locale with React Intl?

To access the current locale with React Intl, you can use the injectIntl higher-order component provided by the library. Here’s a step-by-step guide:

1. First, make sure you have the react-intl package installed. You can install it using npm by running the following command:

npm install react-intl

2. Import the necessary dependencies in the file where you want to access the locale. Typically, this would be a component where you render your internationalized content. Here’s an example:

import React from 'react';
import { injectIntl } from 'react-intl';

3. Wrap your component with the injectIntl higher-order component. This will provide the intl object as a prop to your component, which has several useful methods and properties, including locale.

 Here’s an example of wrapping a functional component:

const MyComponent = ({ intl }) => {
  const currentLocale = intl.locale;
  // Use the 'currentLocale' variable in your component logic  return (
    // Render the localized content here
export default injectIntl(MyComponent);

4. Now, you can access the current locale through the intl object in your component. In the example above, we store the current locale in the currentLocale variable and use it in our component logic.

By following these steps, you should be able to access the current locale using React Intl in your application.

Is it recommended to use CSS In JS technique in React?

The decision to use CSS in JS technique, also known as CSS-in-JS, in React depends on various factors and preferences. CSS in JS is a modern approach where CSS styles are written and managed within JavaScript code. Instead of writing separate CSS files, you write your styles directly in your React components.Advantages of CSS in JS:

1. Component-centric: CSS in JS allows you to write and manage styles specific to each component. This helps in creating more modular and reusable code.

2. Scoped styles: With CSS in JS, styles are automatically scoped to the individual components, reducing the chances of class name collisions and making styling more encapsulated.

3. Dynamic styling: Since you have access to the full power of JavaScript, you can dynamically generate styles based on props or state, resulting in more flexible and interactive components.

4. Improved performance: Some CSS in JS libraries utilize techniques like automatic code splitting and server-side rendering, which can improve performance by reducing the amount of unused CSS being sent to the browser.

5. Developer experience: Writing CSS in JS can provide a more streamlined development experience by allowing you to use JavaScript features like variables, functions, and imports, which can increase code maintainability and readability.

However, it’s important to consider the potential drawbacks as well:

1. Learning curve: If you’re not familiar with CSS in JS libraries like Styled Components or Emotion, there might be a learning curve involved in understanding their syntax and concepts.

2. Tooling support: While CSS in JS has gained popularity, it may not have the same level of tooling support as traditional CSS. It’s essential to evaluate the available tooling (e.g., IDE extensions, linting) before adopting CSS in JS.

3. Performance concerns: Depending on the library and implementation, CSS in JS techniques can introduce some overhead, especially for larger applications. Be mindful of the additional JavaScript payload and evaluate the performance impact.

4. Team familiarity: If you’re working in a team, it’s crucial to assess the familiarity and comfort level of your teammates with CSS in JS. Ensure that everyone can understand and maintain the codebase effectively.

Ultimately, whether to use CSS in JS or traditional CSS depends on your specific project requirements, the team’s expertise, and personal preference. It’s always a good idea to evaluate the trade-offs and experiment with small parts of your application before committing fully.

What is Concurrent Rendering in ReactJS?

Concurrent Rendering in ReactJS is a feature that allows React to work on breaking down large rendering tasks into smaller, manageable chunks. Traditionally, React worked in a synchronous manner, where it would block the main thread until the entire component tree was rendered.

With Concurrent Rendering, React can now split the rendering work into smaller units called “fibers” and work on them in a concurrent manner. This means that instead of waiting for one component to finish rendering before moving on to the next, React can pause and switch between rendering multiple components, making use of idle time in the browser.

The goal of Concurrent Rendering is to improve the overall performance and user experience by making React more responsive, especially on low-powered devices or in situations where the main thread is busy with other tasks.

One important aspect of Concurrent Rendering is the ability to prioritize rendering work based on what is most important to the user. For example, a large list of items might be less important to render immediately compared to a critical UI element. Concurrent Rendering allows React to decide which parts of the UI should be prioritized and rendered first.

To achieve Concurrent Rendering, React introduced a new architecture called “Fiber Reconciliation” which replaces the old stack-based mechanism. It allows React to interrupt and resume rendering work, and also enables scheduling and prioritization of tasks.

By leveraging Concurrent Rendering, React can deliver a more fluid and performant user interface, with better responsiveness and perceived speed, ultimately enhancing the overall user experience.