Reactjs Interview Questions And Answers For Advanced Practitioners

While there are numerous front-end frameworks and libraries that serve as super tools for challenge improvement, the 2021 State of JavaScript survey revealed ReactJS as the most used front-end web development technology. This highlights why there may be a non-stop demand for qualified developers well-versed in Facebook’s distinguished JavaScript library. Similarly, there are plenty of contenders aware of this and seeking to work as ReactJS developers for elite agencies.

Knowing the quantity of work it takes to ace those interviews, we have provided you with this compilation of questions with the best probability of being asked as a senior developer candidate. Going through these popular questions will give you the best chance of answering most of the questions asked in a React.Js interview very well.

React JS Interview Questions for Experienced Professionals

Following are some of the React.js advanced interview questions that can be beneficial for senior developers:

What is Redux?

Redux helps facilitate the development process by providing predictable management of state changes. Incorporating this famous tool with React allows for efficient control of an application’s centralized store via dispatched actions and reducers.

What is portals in React.

Portal is a function that renders children components into DOM that exists outside the DOM hierarchy of parent components. It is a convenient way to render components and is good to use for elements that require escaping the DOM default hierarchy.

List the benefits of Redux.

The advantages of Redux consist of centralized state control, predictable state updates, improved debugging with time-traveling, middleware for handling side effects, and support for hot-reloading.

What is error boundaries in React.

The component that detects javascript errors within the child component tree is known as error boundaries. It facilitates logging these errors and displaying the fallback UI instead of crashing the whole component.

The following example shows an Error Boundary aspect that shows a fallback h1 and logs the error.

class ErrorBoundary extends React.Component {
  constructor(props) {
    super(props);
    this.state = { hasError: false };
  }

  static getDerivedStateFromError(error) {
    return { hasError: true };
  }
  
  componentDidCatch(error, errorInfo) {
    console.log(error, errorInfo);
  }
  
  render() {
    if (this.state.hasError) {
      // fallback UI
      return <h1>Something is wrong.</h1>;
    }
    return this.props.children; 
  }
}

The element can then be used to detect all of the errors within the child component.

<ErrorBoundary>
<child />
</ErrorBoundary>

What is React Profiler and its uses.

The cost of rendering React application is measured via React profiler. It helps the developer identify the components of the utility that require assistance and are slow. It may be introduced everywhere inside the component to measure the rendering cost.

The code below What iss how the profiler aspect measures the rendering cost of the navigation component:

render(
  <App>
    <Profiler id=”Navigation” onRender={callback}>
      <Navigation {…props} />
    </Profiler>
    <Main {…props} />
  </App>
)

What are React Fragments?

Users of earlier versions of react will remember that it used to complain that two JSX tags which were not enclosed within a surrounding div were not considered valid JSx. Newer versions of React solved this problem with Fragments.

React fragments create a set of child components without requiring a true enclosing tag. It allows the person to return more than one component without any additional wrapping. They are denoted with the aid of an open empty tag <> and a closed empty tag </>

The code beneath shows the running of React fragments:

function Columns() {
  return (
    <>
      <td>Column A</td>
      <td>Column B</td>
    </>
  );
}

How can you modularize code in React?

You can modularize code in React by dividing it into reusable components that have precise functionalities. It makes debugging and updating easier, as well as paving the way for scalability in future development efforts.

What is React Router in element?

React router is a tool for dealing with routing in web applications. It allows switching among various elements without requiring a web page reload. Declarative routing is offered, enabling programmers to outline routes as components and render them in keeping with the current URL. Numerous routing capabilities, which include nested routes, route parameters, query parameters, and redirects, are supported by React router. It combines seamlessly with React, making it simple to create SPAs with many views and dynamic routing.

What is data flow in a React-Redux utility?

React-Redux applications comply with a strict unidirectional information flow sample that relies on caused actions and ensues nation updates through the Redux store. Any connected components obtain the state-of-the-art updated state as propagated by way of those adjustments.

What is the difference between React Context and Redux?

React consists of its personal function called React Context, which allows records to be exceeded amongst components without explicitly utilizing props. Redux is a standalone library used mostly for state control that incorporates extra tools, like middleware and a global store.

How are decorators used in React?

React provides decorators as an effective way of optimizing components by providing extra functionality. By adding a decorator before the issue announcement, the usage of “@”, developers can streamline their code and gain clarity in their implementation.

How is testing in React applications done?

React applications can undergo rigorous checking with the aid of specialized frameworks, including Jest and Enzyme. Developers benefit from the handy suite of utilities provided with the aid of these frameworks, which encompass effective simulation competencies for any component interaction.

What are the different methods to pass data among components in React?

React furnishes the front-end developers with several strategies for passing data among different elements or portions of web software. Among these methods are props that facilitate the passage of data from parent element into their child counterparts; callbacks that permit children components to send information up the hierarchy chain; context that depends on the ancestral relationships among unique components; and Redux store supplying access to the global state.

How is React Router different from Conventional Router?

React Router serves as a special useful resource for single-web page applications developed with React. It makes use of components in defining routes, which sets it apart from conventional routers that depend especially on URLs to address routing tasks in server-side apps.

How are data passed on from the child to the parent component?

In React, transmitting data from a child instance to its overseeing parent incorporates a pre-current callback feature. The stated feature is brought about by passing props through the parent component and necessitates having the situation facts handed over as arguments at some point of implementation.

What is the difference between setState and replaceState methods.

Managing factor states in React includes deciding on one of two strategies: “setState” and “replaceState”. When updating a present-day object in State, developers commonly use “setState.” However, while creating an entirely clean profile from scratch is required in place of simply amending small details of an already-gifted one,  “replaceState” is used.

What is Stateful and Stateless Components?

Stateful components control their very own inner states, which can be altered via setState(). Stateless components don’t have any inherent states; however, as an alternative, they depend entirely on the props handed in by different parts of your application.

How is the state with values that depend on the current state updated?

React’s `setState` technique allows developers to adjust factor states efficiently. Moreover, these changes may be made in conjunction with a callback utilizing modern and former state data so that updates rely upon these facts.

How is the element re-rendered without calling setState?

To initiate a re-render of the component, it isn't always needed to invoke the'setState' technique. Instead, you'll, in reality, update the props passed to the component from the parent. This will trigger a re-render primarily based on the new prop values.

How does a person set key names inside the state object?

The names of significance within the state object are decided by using the properties assigned through users in the course of the initialization of an component’s state or when they alter its state with `setState` later.

What is the motive of the useEffect hook?

React’s useEffect is a flexible hook that makes it viable to execute aspect outcomes in practical components. With this hook, data fetching and event subscriptions are made easy. It runs after each render.

What is stateless components?

React’s stateless components, additionally referred to as functional ones, do not have an inner state and are defined entirely as regular functions. They depend on entering data from props, and their role is centered on rendering tasks.

What is the cause of the useRefs hook?

The useRef hook proves beneficial in offering a changeable value that endures throughout more than one component render. Its functionality is often used by developers to get or keep references to DOM elements while also maintaining non-static values that don’t result in re-renders.

How can you build a custom hook??

In React, crafting custom hooks entails taking reusable code and changing it right into a function with a “use” prefix. These hooks have the functionality of using different hooks and can be applied to several components to grant distinct functionalities.

What is pure components?

React has pure components that completely re-render while their props or states undergo modifications. They do that to ward off pointless re-renders and check for alterations to the props and state.

What is the approach to re-render the view while the viewport size is modified?

To re-render the view while the viewport size changes, do the following:

• Look for the “resize” event at the window object.
• In the event handler, replace the vital variables or state associated with the view.
• Trigger a re-render of the view using the updated variables or state.

Is static typing possible in React Hook? Explain your answer.

Yes, static typing is possible in React Hooks with the use of TypeScript. TypeScript affords type annotations and inferences for React components and hooks, helping to seize type errors at some point in development.

Why is Router required in React?

To permit navigation among various perspectives or components, React uses a router. This allows a multi-web page experience within a single-page application by basing the switching procedure on the current URL.

What is StrictMode in React.

This tool helps spotlight any possible problems in an application. It is used as a component but does not create any visible UI inside the DOM. One can allow strict mode for the utility by wrapping the components in  React.StrictMode.

The code below indicates the operation of strict mode:

import React from ‘React’;
function Application() {
  return (
    <div>
      <Header />
      <React.StrictMode>
        <div>
          <Content />
        </div>
      </React.StrictMode>
    </div>
  );
}

How do you take care of forms in React?

React allows for forms to be controlled through controlled components, in which shape inputs are connected to nation variables and changed through occasion handlers. Alternatively, libraries, including Formik, may be employed for streamlined form control that carries superior functionality, along with validation and form submission.

Conclusion

The React JS interview questions strongly depend on the qualifications of the candidate. It also varies in line with the position that the candidate has applied for. Therefore, having a strong understanding of React JS is vital, especially in this era-driven global and competitive job market.