Top 100 Advanced React Interview Questions & Answers 2021

In this guide, we have come up with certain questions that will help you to prepare for your react questions. It’s very important that you learn about the company asked questions and prepare yourself according to that. So take a look at the list of react interview questions and prepare yourself for your next interview.

React Interview Questions And Answers

Q1.What is React?

Ans-

React is a front-end JavaScript library developed by Facebook in 2011.

It follows the component based approach which helps in building reusable UI components.

It is used for developing complex and interactive web and mobile UI.

Even though it was open-sourced only in 2015, it has one of the largest communities supporting it.

Q2.What are the features of React?

Ans-

Major features of React are listed below:

It uses the virtual DOM instead of the real DOM.

It uses server-side rendering.

It follows uni-directional data flow or data binding.

Q3.List some of the major advantages of React.

Ans-

Some of the major advantages of React are:

It increases the application’s performance

It can be conveniently used on the client as well as server side

Because of JSX, code’s readability increases

React is easy to integrate with other frameworks like Meteor, Angular, etc

Using React, writing UI test cases become extremely easy

Q4.What are the limitations of React?

Ans-

Limitations of React are listed below:

React is just a library, not a full-blown framework

Its library is very large and takes time to understand

It can be little difficult for the novice programmers to understand

Coding gets complex as it uses inline templating and JSX

Q5.What do you understand from “In React, everything is a component.”

Ans-

Components are the building blocks of a React application’s UI. These components split up the entire UI into small independent and reusable pieces. Then it renders each of these components independent of each other without affecting the rest of the UI.

Q6.Explain the purpose of render() in React.

Ans-

Each React component must have a render() mandatorily. It returns a single React element which is the representation of the native DOM component. If more than one HTML element needs to be rendered, then they must be grouped together inside one enclosing tag such as

, ,

etc. This function must be kept pure i.e., it must return the same result each time it is invoked.

Q7.How can you embed two or more components into one?

Ans-

We can embed components into one in the following way:

class MyComponent extends React.Component{

    render(){

        return(

Hello

               

           

        );

    }

}

class Header extends React.Component{

    render(){

        return

Header Component

   };

}

ReactDOM.render(

    , document.getElementById(‘content’)

);

Q8.What is Props?

Ans-

Props is the shorthand for Properties in React. They are read-only components which must be kept pure i.e. immutable. They are always passed down from the parent to the child components throughout the application. A child component can never send a prop back to the parent component. This help in maintaining the unidirectional data flow and are generally used to render the dynamically generated data.

Q9.What are the different phases of React component’s lifecycle?

Ans-

There are three different phases of React component’s lifecycle:

Initial Rendering Phase: This is the phase when the component is about to start its life journey and make its way to the DOM.

Updating Phase: Once the component gets added to the DOM, it can potentially update and re-render only when a prop or state change occurs. That happens only in this phase.

Unmounting Phase: This is the final phase of a component’s life cycle in which the component is destroyed and removed from the DOM.

Q10.Explain the lifecycle methods of React components in detail.

Ans-

Some of the most important lifecycle methods are:

componentWillMount() – Executed just before rendering takes place both on the client as well as server-side.

componentDidMount() – Executed on the client side only after the first render.

componentWillReceiveProps() – Invoked as soon as the props are received from the parent class and before another render is called.

shouldComponentUpdate() – Returns true or false value based on certain conditions. If you want your component to update, return true else return false. By default, it returns false.

componentWillUpdate() – Called just before rendering takes place in the DOM.

componentDidUpdate() – Called immediately after rendering takes place.

componentWillUnmount() – Called after the component is unmounted from the DOM. It is used to clear up the memory spaces.

Q11.What is an event in React?

Ans-

In React, events are the triggered reactions to specific actions like mouse hover, mouse click, key press, etc. Handling these events are similar to handling events in DOM elements. But there are some syntactical differences like:

Events are named using camel case instead of just using the lowercase.

Events are passed as functions instead of strings.

The event argument contains a set of properties, which are specific to an event. Each event type contains its own properties and behavior which can be accessed via its event handler only.

Q12.What are Higher Order Components(HOC)?

Ans-

Higher Order Component is an advanced way of reusing the component logic. Basically, it’s a pattern that is derived from React’s compositional nature. HOC are custom components which wrap another component within it. They can accept any dynamically provided child component but they won’t modify or copy any behavior from their input components. You can say that HOC are ‘pure’ components.

Q13.What can you do with HOC?

Ans-

HOC can be used for many tasks like:

Code reuse, logic and bootstrap abstraction

Render High jacking

State abstraction and manipulation

Props manipulation

Q14.What are Pure Components?

Ans-

Pure components are the simplest and fastest components which can be written. They can replace any component which only has a render(). These components enhance the simplicity of the code and performance of the application.

Q15.What is the significance of keys in React?

Ans-

Keys are used for identifying unique Virtual DOM Elements with their corresponding data driving the UI. They help React to optimize the rendering by recycling all the existing elements in the DOM. These keys must be a unique number or string, using which React just reorders the elements instead of re-rendering them. This leads to increase in application’s performance.

Q16.What were the major problems with MVC framework?

Ans-

Following are some of the major problems with MVC framework:

DOM manipulation was very expensive

Applications were slow and inefficient

There was huge memory wastage

Because of circular dependencies, a complicated model was created around models and views

React Interview Questions

1.What is React?

2.What are the major features of React?

3.What is JSX?

4.What is the difference between Element and Component?

5..How to create components in React?

6.When to use a Class Component over a Function Component?

7.What are Pure Components?

8.What is state in React?

9.What are props in React?

10.What is the difference between state and props?

11.Why should we not update the state directly?

12.What is the purpose of callback function as an argument of setState()?

13.What is the difference between HTML and React event handling?

14.How to bind methods or event handlers in JSX callbacks?

15.How to pass a parameter to an event handler or

callback?

16.What are synthetic events in React?

17.What is inline conditional expressions?

18.What are “key” props and what is the benefit of using them in arrays of elements?

19.What is the use of refs?

20.How to create refs?

React Interview Questions For Freshers

21.What are forward refs?

22.Which is preferred option with in callback refs and findDOMNode()?

23.Why are String Refs legacy?

24.What is Virtual DOM?

25.How Virtual DOM works?

26.What is the difference between Shadow DOM and Virtual DOM?

27.What is React Fiber?

28.What is the main goal of React Fiber?

29.What are controlled components?

30.What are uncontrolled components?

31.What is the difference between createElement and cloneElement?

32.What is Lifting State Up in React?

33.What are the different phases of component lifecycle?

34.What are the lifecycle methods of React?

35.What are Higher-Order components?

36.How to create props proxy for HOC component?

37.What is context?

38.What is children prop?

39.How to write comments in React?

40.What is the purpose of using super constructor with props argument?

React Interview Questions For Experienced

41.What is reconciliation?

42.How to set state with a dynamic key name?

43.What would be the common mistake of function being called every time the component renders?

44.Is lazy function supports named exports??

45.Why React uses className over class attribute?

46.What are fragments?

47.Why fragments are better than container divs?

48.What are portals in React?

49.What are stateless components?

50.What are stateful components?

51.How to apply validation on props in React?

52.What are the advantages of React?

53.What are the limitations of React?

54.What are error boundaries in React v16

55.How error boundaries handled in React v15?

56.What are the recommended ways for static type checking?

57.What is the use of react-dom package?

58.What is the purpose of render method of react-dom?

59.What is ReactDOMServer?

60.How to use InnerHtml in React?

61.How to use styles in React?

62.How events are different in React?

63.What will happen if you use setState in constructor?

Conclusion:

These are the best react interview questions. I hope you guys like our react interview questions list for freshers & experienced. If you have any question or suggestion then just comment below or contact us.

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