Ernst & Young React Developer Interview Questions and Answers

Round duration - 60 Minutes
Round difficulty - Medium

This was a preety intense round revolving mainly around the core concepts of JavaScript . I was confident about my
skills in JavaScript as I already had some projects in JS and I also completed the Guided Path of JS in CodeStudio
which boosted my preparation and helped me crack these Frontend Interviews.

Q1. What are callbacks in JavaScript?
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Q2. Can you explain hoisting in JavaScript?
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Q3. What are closures in JavaScript?
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Q4. What is the difference between slice and splice in JavaScript?
Ans. 
slice() returns a shallow copy of a portion of an array without modifying the original array, while splice() changes the contents of an array by removing or replacing existing elements.
• slice() does not modify the original array, while splice() does

• slice() returns a new array, while splice() returns the removed elements

• slice() takes start and end index as arguments, while splice() takes start index, number of elements t...read more
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Q5. What is a first-class function in JavaScript?
Ans. 
A first-class function in JavaScript is a function that can be treated like any other variable.
• Can be passed as an argument to other functions

• Can be returned from other functions

• Can be assigned to variables

• Can be stored in data structures
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Q6. How would you sort an array of integers in JavaScript?
Ans. 
Use the built-in sort() method to sort an array of integers in JavaScript.
• Use the sort() method with a compare function to sort the array in ascending order.

• For descending order, modify the compare function to return b - a instead of a - b.

• Example: const numbers = [4, 2, 5, 1, 3]; numbers.sort((a, b) => a - b);
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Q7. 
Covid Vaccination Distribution Problem
As the Government ramps up vaccination drives to combat the second wave of Covid-19, you are tasked with helping plan an effective vaccination schedule. Your goal is...read more
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Round duration - 60 Minutes
Round difficulty - Medium

In this round, I was asked questions from React and Redux. Since I already had prior experience in working with React
and Redux , I answered most of the questions correctly and was preety much confident about passing this round.

Q1. What are the differences between a class component and a functional component in ReactJS?
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Q2. What are the differences between stateless and stateful components in ReactJS?
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Q3. What is the diffing algorithm in ReactJS?
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Q4. What is reconciliation in ReactJS?
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Q5. What are props in React?
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Q6. What are the advantages of using Redux?
Ans. 
Redux helps manage application state in a predictable way.
• Centralized state management

• Predictable state changes with actions and reducers

• Time-travel debugging with Redux DevTools

• Ecosystem of middleware for additional functionality
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Q7. What are the key differences between mapStateToProps() and mapDispatchToProps() in Redux?
Ans. 
mapStateToProps() is used to access the Redux state in a component, while mapDispatchToProps() is used to dispatch actions to update the state.
• mapStateToProps() is used to access the Redux state and return data as props for a component.

• mapDispatchToProps() is used to dispatch actions to update the Redux state.

• mapStateToProps() is a function that takes the current state as an argument and returns an object with props th...read more
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Q8. What is the Combine Reducer in Redux?
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Q9. How is Relay different from Redux?
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Q10. How can we structure the top-level directories in Redux?
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Round duration - 30 Minutes
Round difficulty - Easy

This was a Technical Cum HR round where I was first asked some basic principles around Frontend Web Development
and then we discussed about my expectations from the company , learnings and growth in the forthcomig years. I would
suggest be honest and try to communicate your thoughts properly in these type of rounds to maximise your chances of
getting selected.

Q1. What do you know about the company?
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Q2. Why should we hire you?
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