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Web / ReactJS Interview questions

Why do we need to use keys in Lists?

A key is a unique identifier and it is used to identify which items have changed, been updated or deleted from the lists. It also helps to determine which components need to be re-rendered instead of re-rendering all the components every time. Therefore, it increases performance, as only the updated components are re-rendered.

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What is React? Advantages of using ReactJS. Explain Virtual DOM. What is JSX? Who created ReactJS? is ReactJS an MVC framework? What are the major features of React? Mention a few React hooks. What is useContext in react? What is context in React? What is the need for Babel in React? What are React fragments? How do you specify CSS class for HTML elements in React? What are Custom hooks in React? What is PropTypes in react? When does React decide to re-render a component? Difference between using "useState" hook and just a variable in React. How do you create a Class component in React? What are the lifecycle methods of class Component in React? What is the role of constructor() in React components? Difference between Shadow DOM and Virtual DOM. Difference between Element and Component. When to use a Class Component over a Function Component? What is React PureComponent? Difference between state and props in React. Why should we not update the react component state directly? What are synthetic events in React? What is React Fiber? What are controlled components? Difference between createElement and cloneElement. What is Lifting State Up in React? How to write comments in React? What is Error Boundaries in React? What is ReactDOMServer? Differentiate between Real DOM and Virtual DOM. What is the purpose of render() in React. How do I force a React component to re-render? How is React different from Angular? What are Higher-order components in React? Why do we need to use keys in Lists? Difference between Dumb components and Smart components in React. How do you create a form in React? Advantages of using REDUX. Is setState asynchronous? What is prop drilling? Explain Redux Thunk. What are default props in React? What are events in React? Advantages of React hooks. What is memoize in React? How do I implement shouldComponentUpdate using React hooks? Explain useRef hook in React. What is Strict Mode in React? What is the main difference between useRef and useState hooks? Difference between declarative and imperative programming? What is "Render Props" pattern/technique in React? What is unidirectional data flow in react? What is "Lift State Up" pattern in React? What are React controlled components and uncontrolled components? What is the purpose of REF in react? What is a key in React? Why is "class" attribute is "className" in React? How would delay an API call until the component has mounted? Can I use ternary (or) && Operator to conditionally render React components?
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