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React interview questions

React interview questions.

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  • 1.

    How does React work?

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  • 2.

    What is context?

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  • 3.

    What is virtual DOM?

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  • 4.

    What is props in ReactJS?

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  • 5.

    What is the use of refs?

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  • 6.

    What is JEST?

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  • 7.

    What are the advantages of ReactJS?

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  • 8.

    What is ReactJS?

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  • 9.

    How to write comments in ReactJS?

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  • 10.

    How would you write an inline style in React?

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  • 11.

    What are the major features of ReactJS?

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  • 12.

    What are props in React?

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  • 13.

    What are the differences between a class component and functional component?

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  • 14.

    Where in a React component should you make an AJAX request?

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  • 15.

    What is the difference between state and props?

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  • 16.

    What is the difference between a Presentational component and a Container component?

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  • 17.

    What are refs used for in React?

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  • 18.

    What's the difference between a controlled component and an uncontrolled one in React?

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  • 19.

    What are controlled components?

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  • 20.

    What is state in ReactJS?

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  • 21.

    When to use a Class Component over a Functional Component?

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  • 22.

    What does it mean for a component to be mounted in React?

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  • 23.

    How do we pass a property from a parent component props to a child component?

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  • 24.

    What are fragments?

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  • 25.

    When rendering a list what is a key and what is it's purpose?

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  • 26.

    How to create refs?

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  • 27.

    What happens when you call setState?

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  • 28.

    What are stateful components?

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  • 29.

    How would you prevent a component from rendering in React?

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  • 30.

    What is JSX?

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  • 31.

    How error boundaries handled in React (15)?

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  • 32.

    Where is the state kept in a React + Redux application?

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  • 33.

    What are the limitations of ReactJS?

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  • 34.

    What is the difference between React Native and React?

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  • 35.

    What are stateless components?

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  • 36.

    How is React different from AngularJS (1.x)?

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  • 37.

    What is the point of Redux?

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  • 38.

    Why is it necessary to capitalize the components?

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  • 39.

    What is the difference between state and props?

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  • 40.

    What is Flow?

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  • 41.

    How to create components in ReactJS?

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  • 42.

    What is the purpose of callback function as an argument of setState?

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  • 43.

    What are portals in ReactJS?

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  • 44.

    How to pass a parameter to an event handler or callback?

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  • 45.

    What’s the difference between an "Element" and a "Component" in React?

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  • 46.

    What happens during the lifecycle of a React component?

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  • 47.

    What is Flux?

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  • 48.

    What is the difference between component and container in react Redux?

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  • 49.

    What is inline conditional expressions?

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  • 50.

    How do you prevent the default behavior in an event callback in React?

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  • 51.

    What is reconciliation?

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  • 52.

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

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  • 53.

    What happens when you call "setState"?

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  • 54.

    Describe how events are handled in React.

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  • 55.

    What is the difference between Element and Component?

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  • 56.

    What are Higher-Order components?

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  • 57.

    Name the different lifecycle methods.

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  • 58.

    What is a higher order component?

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  • 59.

    What is JSX?

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  • 60.

    What is state in react?

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  • 61.

    What are controlled components?

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  • 62.

    What is a store in redux?

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  • 63.

    How would you prevent a component from rendering?

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  • 64.

    What don't you like about React?

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  • 65.

    What advantages are using arrow functions?

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  • 66.

    Why is it advised to pass a callback function to setState as opposed to an object?

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  • 67.

    What's the typical pattern for rendering a list of components from an array of data?

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  • 68.

    What are PropTypes in React?

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  • 69.

    What are Pure Components?

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  • 70.

    What are the advantages of React over VueJS?

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  • 71.

    Name some popular Flux Libraries

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  • 72.

    What's the typical flow of data like in a React + Redux app?

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  • 73.

    What are synthetic events in ReactJS?

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  • 74.

    What's an alternative way to avoid having to bind to this in event callback methods?

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  • 75.

    What are some limitations of things you shouldn't do in the component's render method?

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  • 76.

    How to bind methods or event handlers in JSX callbacks?

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  • 77.

    What is useState() in React?

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  • 78.

    What is the difference between createElement and cloneElement?

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  • 79.

    Why fragments are better than container divs?

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  • 80.

    What is prop drilling and how can you avoid it?

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  • 81.

    What is an action?

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  • 82.

    What is the point of shouldComponentUpdate() method?

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  • 83.

    What are forward refs?

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  • 84.

    What do these three dots (...) in React do?

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  • 85.

    How do you tell React to build in Production mode and what will that do?

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  • 86.

    What are typical middleware choices for handling asynchronous calls in Redux?

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  • 87.

    What are the lifecycle methods of ReactJS?

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  • 88.

    What are the different phases of ReactJS component lifecycle?

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  • 89.

    What is Key and benefit of using it in lists?

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  • 90.

    What's the difference between an Element and a Component in React?

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  • 91.

    What is the difference between ShadowDOM and VirtualDOM?

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  • 92.

    Why do class methods need to be bound to a class instance?

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  • 93.

    What are stateless components?

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  • 94.

    What is ReactDOM?

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  • 95.

    What is children prop?

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  • 96.

    Why ReactJS uses className over class attribute?

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  • 97.

    What are React Hooks?

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  • 98.

    What does "shouldComponentUpdate" do and why is it important?

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  • 99.

    What's the difference between a "smart" component and a "dumb" component?

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  • 100.

    What is the render method for?

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  • 101.

    What is Lifting State Up in ReactJS?

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  • 102.

    Why should not we update the state directly?

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  • 103.

    How to set state with a dynamic key name?

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  • 104.

    What's the difference between useRef and createRef?

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  • 105.

    What is StrictMode in React?

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  • 106.

    What is the alternative of binding this in the constructor?

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  • 107.

    What is the difference between createElement and cloneElement?

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  • 108.

    What is the point of using keys in React?

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  • 109.

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

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  • 110.

    What are advantages of using React Hooks?

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  • 111.

    What can you tell me about JSX?

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  • 112.

    What is the difference between HTML and React event handling?

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  • 113.

    What are error boundaries in ReactJS (16)?

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  • 114.

    What is reconciliation in React?

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  • 115.

    What are uncontrolled components?

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  • 116.

    What is equivalent of the following using React.createElement?

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  • 117.

    Given the code defined above, can you identify two problems?

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  • 118.

    What is a reducer?

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  • 119.

    What is the purpose of super(props)?

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  • 120.

    What is "Children"?

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  • 121.

    Why would you eject from create-react-app?

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  • 122.

    What is the difference between ReactJS and Angular?

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  • 123.

    Explain the Virtual DOM concept in React.

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  • 124.

    What is the difference between a controlled component and an uncontrolled component?

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  • 125.

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

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  • 126.

    What are the recommended ways for static type checking?

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  • 127.

    Describe Flux vs MVC?

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  • 128.

    Why would you use forceUpdate in a React component?

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  • 129.

    What is React Fiber?

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  • 130.

    What are some recent changes in the React library (e.g. in version 14, 15)?

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  • 131.

    Why does React use SyntheticEvents?

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  • 132.

    How would you go about investigating slow React application rendering?

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  • 133.

    What's a pure functional component in React?

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  • 134.

    What is the second argument that can optionally be passed to setState and what is its purpose?

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  • 135.

    When is it important to pass props to super(), and why?

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  • 136.

    Do Hooks replace render props and higher-order components?

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  • 137.

    Why would you need to bind event handlers to "this"?

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  • 138.

    What is the difference between Flow and PropTypes?

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  • 139.

    What is the difference between using constructor vs getInitialState in React?

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  • 140.

    Why are String Refs legacy?

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  • 141.

    Are you familiar with Flux?

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  • 142.

    What is the React context?

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  • 143.

    Why would you use React.Children.map(props.children, () => ) instead of props.children.map(() => )?

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  • 144.

    What is mapStateToProps and mapDispatchToProps?

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  • 145.

    How to create props proxy for HOC component?

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  • 146.

    How to conditionally add attributes to React components?

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  • 147.

    Does React re-render all components and sub components every time setState is called?

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  • 148.

    If you need to access the underlying DOM node for a React component, what's the typical way to do this in React?

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  • 149.

    How to apply validation on Props in ReactJS?

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  • 150.

    When would you use StrictMode component in React?

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  • 151.

    What is a Pure Function?

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  • 152.

    Explain some difference between Flux and AngularJS (1.x) approach

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  • 153.

    What is reselect and how it works?

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  • 154.

    What is the key architectural difference between a JavaScript library such as React and a JavaScript framework such as Angular?

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  • 155.

    What is Redux Thunk used for?

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  • 156.

    What is React Fiber?

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  • 157.

    How to use Polymer in ReactJS?

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  • 158.

    How to avoid the need for binding in React?

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  • 159.

    How does React renderer work exactly when we call setState?

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  • 160.

    If you created a React element like Twitter below, what would the component definition of Twitter look like?

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  • 161.

    What is wrong with this code?

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23 Databases interview questions and answers for software engineers

A database is an organized collection of data, generally stored and accessed electronically from a computer system. Where databases are more complex they are often developed using formal design and modeling techniques. Here is a list of coding interview questions on Databases to help you g...

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21 Concurrency interview questions and answers for software engineers

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