ReactJS Interview Questions Part-5

Why ReactDOM is separated from React?

ReactDOM is a separate library within the React ecosystem that focuses specifically on rendering and manipulating the user interface in a web browser environment. While React itself is designed to be platform-agnostic and can be used to build user interfaces for not just web applications but also mobile and desktop applications, ReactDOM is tailored specifically for web browsers.

Separating ReactDOM from React allows for a more modular approach to development, enabling developers to choose the specific libraries they need based on their project requirements. It also allows React to be more lightweight and flexible, as developers can opt to use React without ReactDOM if they’re not targeting web browser environments.

By keeping ReactDOM as a separate library, it can focus solely on the task of efficiently updating the DOM (Document Object Model) in response to changes in React components. This separation also makes it easier to maintain and update both libraries separately, allowing for faster bug fixes and feature additions.

Overall, separating ReactDOM from React provides developers with more flexibility and modularity when building user interfaces, while also keeping each library focused on its respective responsibilities.

What are the exceptions on React component naming in ReactJS?

In ReactJS, there are a few exceptions to the naming conventions for component names:

1. Components that render HTML elements: When you create a component that renders an HTML element, you should use the name of the HTML element as the component name in lowercase. For example, if you have a component that renders a you should name it Div or div rather than MyDiv or myDiv.

2. Components that are part of a third-party library: If you’re using a third-party library that provides its own components, you should follow the naming conventions specified by that library. For example, if you’re using the Material-UI library, you would use names like Button or AppBar for their components, even if they don’t adhere to the usual naming conventions.

3. Higher-order components (HOCs): HOCs are components that wrap other components and enhance their functionality. When naming HOCs, it’s common to prefix their names with “with” followed by the feature they provide. For example, if you have an HOC that adds authentication functionality, you might name it withAuth or withAuthentication.

4. Components that represent pages or routes: If you’re creating a component that represents a specific page or route in your application, you can use a descriptive name that reflects the purpose of that page or route. For example, if you have a component that represents the login page, you might name it LoginPage or Login.

Remember, it’s important to be consistent with your naming conventions within your project so that your codebase remains clean and maintainable.

What do you understand by Single source of truth

Single Source of Truth (SSOT) is a principle in data management that advocates for the concept of having one centralized, authoritative source of data that can be used across an organization. This means that all stakeholders within an organization rely on this single source for accurate and up-to-date information, ensuring consistency and reducing the risk of conflicting or outdated data.

By having a single source of truth, organizations can improve decision-making, increase operational efficiency, and enhance data integrity. It helps in minimizing data duplication, inconsistencies, and errors that may arise from using multiple sources of data. Additionally, it promotes transparency, collaboration, and trust among teams by providing a reliable foundation for analysis and reporting.

Implementing SSOT requires establishing robust data governance practices, ensuring data quality, and implementing appropriate tools and technologies to maintain and manage the central repository of data effectively.

What are the advantages of formik over redux form library in ReactJS?

Formik and Redux Form are both popular form management libraries in ReactJS, each with its own set of advantages. Here are some advantages of Formik over Redux Form:

1. Simplicity and ease of use: Formik focuses on simplicity and provides a straightforward API that is easy to understand and work with. It aims to make form management as simple as possible by handling common form-related tasks out of the box.

2. Built-in validation: Formik offers built-in support for form validation, allowing you to easily define validation rules for your form fields. It provides a simple and intuitive way to specify validation schemas and handle form submission errors.

3. Local component state: Formik manages form state internally within the component itself, which eliminates the need for additional Redux boilerplate code. This simplifies the overall code structure and reduces the learning curve for developers who are new to Redux.

4. Performance: Formik is designed to have a smaller footprint compared to Redux Form. It achieves this by avoiding unnecessary re-renders and optimizing performance through various techniques such as memoization.

5. Integration with React Hooks: Formik has extensive support for React Hooks, making it easier to integrate with functional components. It allows you to leverage the power of Hooks to manage form state and simplify your code.

6. Minimal dependencies: Formik has minimal dependencies, which means you don’t have to include extra libraries in your project. This can be beneficial in terms of reducing bundle size and avoiding potential compatibility issues with other libraries.

7. Active community and ongoing development: Formik has a large and active community, with ongoing development and regular updates. This ensures that you’ll have access to bug fixes, new features, and community support when working with Formik.

It’s important to note that while Formik may be advantageous in certain scenarios, Redux Form is still a powerful and widely used form library with its own strengths. The choice between the two ultimately depends on the specific requirements and preferences of your project.

What is Test Renderer package in React?

The Test Renderer package in React is a testing utility provided by React that allows you to render React components into static JSON-like structures called “trees”. These tree structures can be analyzed, traversed, and manipulated in order to test the output of your React components.

Using Test Renderer, you can simulate the rendering of your React components without the need for a full DOM or browser environment. This makes it ideal for testing the structure and behavior of your components in an isolated and predictable manner.With Test Renderer, you can:

1. Render a React component: You can use the create method from the react-test-renderer package to render a React component into a Test Renderer tree. This tree represents the component and its rendered output.

2. Traverse the rendered tree: The Test Renderer tree is a JSON-like structure that you can traverse and examine to assert expectations about the component’s output. You can access specific nodes and properties to check if they match your expectations.

3. Update the tree: Since the Test Renderer tree is a plain JavaScript object, you can modify its properties to simulate user interactions or state changes. This allows you to test how your component responds to different scenarios.

4. Snapshot testing: Test Renderer provides a feature called “snapshot testing” which allows you to save the rendered output of a component as a serialized representation. You can then compare future renders against this snapshot to ensure that the component’s output hasn’t unexpectedly changed.

Overall, the Test Renderer package helps streamline the testing process for React components by offering a lightweight and flexible way to render, inspect, and manipulate their output. It’s especially useful for unit testing individual components in isolation from the rest of your application.

Which is the preferred option with callback refs and findDOMNode() in ReactJS?

In ReactJS, the preferred option for accessing DOM nodes is by using callback refs. The findDOMNode() method, on the other hand, is considered less ideal and discouraged in newer versions of React.

Callback refs allow you to directly reference an individual DOM node or a component instance using a callback function. This callback function is called with the DOM node or component instance as its argument when the component mounts and updates. By using callback refs, you can safely access and manipulate DOM elements within your React components.

On the other hand, findDOMNode() is a method provided by React that returns the underlying DOM node of a mounted component. While it can be useful in some scenarios, it has some drawbacks. It breaks encapsulation by allowing access to the underlying DOM structure, which goes against the principles of React component-based architecture. It also hinders potential performance optimizations since React can’t guarantee that the returned DOM node will remain the same between renders.

Therefore, it is generally recommended to use callback refs over findDOMNode(). Callback refs provide a more explicit and controlled way of accessing DOM nodes within your React components while still adhering to React’s component-based philosophy.

What is NextJS and major features of it in ReactJS?

Next.js is a popular framework for building server-rendered React applications. It provides several key features that enhance the development process and improve the performance of ReactJS applications:

1. Server-Side Rendering (SSR): Next.js allows you to render React components on the server, rather than in the browser. This means that the initial page load is faster since the HTML is already generated on the server, enhancing user experience and SEO.

2. File System Routing: With Next.js, you can create pages by simply placing React components in the “pages” directory. Next.js automatically maps these components to their respective routes, making it easy to create and manage routes in a project.

3. Automatic Code Splitting: Next.js automatically performs code splitting, enabling you to load only the necessary JavaScript code for each page. This helps reduce the initial load time of your application.

4. Hot Module Replacement (HMR): Next.js supports HMR, allowing you to see changes instantly without having to refresh the entire page. It improves the developer experience and makes it quicker to iterate on your code.

5. API Routes: Next.js comes with built-in routing for handling API requests. You can create API endpoints by simply creating files in the “pages/api” directory. This makes it seamless to build serverless functions or backend APIs alongside your React application.

6. Static Site Generation (SSG): Next.js supports both SSR and SSG. You can generate static HTML pages at build-time, which can be useful for content-heavy websites. This approach allows you to build highly performant and scalable applications.

7. TypeScript Support: Next.js has excellent support for TypeScript, providing static type checking out of the box. This helps catch errors during development and enhances code maintainability.

8. Internationalization (i18n): Next.js has built-in support for internationalization, making it easier to localize your application and serve content in multiple languages.

Overall, Next.js simplifies the development process, improves performance, and offers a range of features that enhance the ReactJS ecosystem.

What are the three principles that Redux follows in ReactJS?

Redux follows three core principles when used with ReactJS:

1. Single Source of Truth: Redux maintains a single centralized store that holds the entire application state. This means that all the data for the application is stored in a single JavaScript object, known as the “state”. By having a single source of truth, it becomes easier to manage and update the application state.

2. State is Read-Only: In Redux, the state is immutable and cannot be directly modified. Instead, to update the state, we dispatch actions. Actions are plain JavaScript objects that describe what happened in the application. Reducers, pure functions, then handle these actions and return a new state based on the previous state and the action performed.

3. Changes are Made with Pure Functions: Redux uses pure functions called reducers to update the state. Reducers take in the previous state and an action, and return the new state. They do not modify the original state, but instead create a new copy of it. This ensures that the state remains immutable, making it easier to track changes and debug the application.

By following these principles, Redux provides a predictable state management solution, making it easier to maintain and scale React applications.

Is it prop must be named as render for render props in ReactJS?

No, it is not necessary to name the prop as “render” for render props in ReactJS. The name of the prop can be anything you like; it is just a convention to use the name “render” for clarity and readability.

In ReactJS, render props is a technique where a component accepts a function as a prop, which the component then calls and passes its internal state or other data to this function. The function can then use this data to render some UI. The convention to name this prop as “render” comes from the frequent use of the render method in the component’s lifecycle, where it is responsible for rendering the UI.

However, you are free to use any other name for the prop, as long as you pass a function as the prop value which will receive the relevant data and return the desired UI.

What do you know about controlled and uncontrolled components in React JS?

In ReactJS, components can be categorized as controlled or uncontrolled based on how they handle and manage user input.

1. Controlled Components: 

  • Controlled components are components in which the value of the input elements is controlled by the parent component. 
  • The parent component has full control over the state of the input value, and any changes to the input value are handled through props and state. 
  • To handle user input, you typically use the onChange event, which triggers a callback function that updates the state in the parent component.
  • Since the parent component has full control over the value, it can also validate, manipulate, or perform any other action before updating the input value.

2. Uncontrolled Components: 

  • Uncontrolled components are components in which the value of the input elements is handled by the DOM itself, rather than being managed by React components. 
  • In uncontrolled components, the input elements store their own state internally, and you can access their values using DOM methods like document.getElementById or ref
  • Uncontrolled components are useful when you want a simpler way to handle form inputs without managing state in a parent component. 
  • However, since the state is managed by the DOM, it can become challenging to perform validation or manipulate the input value before using it.

Both controlled and uncontrolled components have their own use cases. Controlled components are commonly used when you need more control and flexibility over the input value, while uncontrolled components offer simplicity for basic form handling.