ERNET India Web Developer Interview Questions and Answers

Q1. Difference between useMemo and useCallback ?
Ans. 
useMemo is used to memoize a value, while useCallback is used to memoize a function.
• useMemo is used to memoize a computed value and recompute it only when its dependencies change.

• useCallback is used to memoize a callback function and prevent unnecessary re-renders.

• Example: useMemo can be used to memoize the result of a complex computation, while useCallback can be used to memoize an event handler function.
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Q2. How we do error handling in js ?
Ans. 
Error handling in JavaScript involves using try-catch blocks, throwing errors, and using error objects.
• Use try-catch blocks to catch errors and handle them gracefully

• Throw errors using the throw keyword to indicate when something goes wrong

• Use error objects like Error, SyntaxError, TypeError, etc. to provide more information about the error

• Handle asynchronous errors using promises and the .catch() method
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Q3. What is Promises ? Write a Polyfill of Promise.all()
Ans. 
Promises are objects representing the eventual completion or failure of an asynchronous operation.
• Promises are used to handle asynchronous operations in JavaScript.

• Promise.all() takes an array of promises and returns a single promise that resolves when all of the input promises have resolved.

• A polyfill for Promise.all() can be implemented using a combination of Promise and Array.prototype.reduce().
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Frontend assignment make the CRUD application using of reactj.s