Cybage 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. Can you explain promises in JavaScript and describe its three states?
Ans. 
Promises in JavaScript represent the eventual completion (or failure) of an asynchronous operation.
• Promises are objects that represent the eventual completion (or failure) of an asynchronous operation.

• They have three states: pending, fulfilled, or rejected.

• A pending promise is one that hasn't been fulfilled or rejected yet.

• A fulfilled promise is one that has been successful.

• A rejected promise is one that has encountere...read more
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Q2. What are callbacks in JavaScript?
Ans. 
Callbacks in JavaScript are functions passed as arguments to other functions to be executed later.
• Callbacks are commonly used in event handling, asynchronous programming, and functional programming.

• They allow for functions to be executed after another function has finished executing.

• Example: setTimeout function takes a callback function as an argument to be executed after a specified time.
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Q3. Can you explain hoisting in JavaScript?
Ans. 
Hoisting is a JavaScript mechanism where variable and function declarations are moved to the top of their containing scope during compilation.
• Variable declarations are hoisted to the top of their scope but not their assignments.

• Function declarations are fully hoisted, meaning they can be called before they are declared.

• Hoisting can lead to unexpected behavior if not understood properly.
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Q4. What are closures in JavaScript?
Ans. 
Closures in JavaScript allow functions to retain access to variables from their parent scope even after the parent function has finished executing.
• Closures are created whenever a function is defined within another function.

• They allow the inner function to access variables from the outer function, even after the outer function has finished executing.

• Closures are commonly used to create private variables and functions in...read more
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Q5. What is a higher order function?
Ans. 
A higher order function is a function that takes one or more functions as arguments or returns a function as its result.
• Higher order functions can be used to create abstractions and compose functions together.

• Examples include map, filter, and reduce functions in JavaScript.

• Higher order functions can also be used for event handling and asynchronous programming.
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Q6. 
Sort Array Problem Statement
Given an array consisting of 'N' positive integers where each integer is either 0, 1, or 2, your task is to sort the given array in non-decreasing order.
Input:
Each input st...read more
Ans. 
Sort an array of positive integers consisting of 0, 1, and 2 in non-decreasing order.
• Use a counting sort approach to count the occurrences of 0s, 1s, and 2s in the array.

• Update the array with the counts of 0s, 1s, and 2s in order to achieve the sorted array.

• Ensure to handle the constraints of the input array elements being 0, 1, or 2.

• Example: Input: [0, 2, 1, 2, 0], Output: [0, 0, 1, 2, 2]
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Q7. 
Swap Two Numbers Problem Statement
Given two integers a and b, your task is to swap these numbers and output the swapped values.
Input:
The first line contains a single integer 't', representing the num...read more
Ans. 
Swap two numbers 'a' and 'b' and output the swapped values.
• Create a temporary variable to store one of the numbers

• Assign the value of 'a' to 'b' and the temporary variable to 'a'

• Output the swapped values as 'b' followed by 'a'
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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?
Ans. 
Class components are ES6 classes that extend from React.Component and have state, while functional components are simple functions that take props as arguments.
• Class components are ES6 classes that extend from React.Component

• Functional components are simple functions that take props as arguments

• Class components have state and lifecycle methods, while functional components do not

• Functional components are easier to read,...read more
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Q2. What is the diffing algorithm in ReactJS?
Ans. 
React uses a diffing algorithm called Virtual DOM to efficiently update the actual DOM.
• React creates a virtual representation of the DOM called Virtual DOM.

• When state or props change, React compares the Virtual DOM with the actual DOM to find the differences.

• React then updates only the parts of the actual DOM that have changed, minimizing re-renders and improving performance.
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Q3. What are the differences between stateless and stateful components in ReactJS?
Ans. 
Stateless components do not have internal state, while stateful components have internal state that can change.
• Stateless components are functional components that do not have internal state

• Stateful components are class components that have internal state that can change

• Stateless components are simpler and easier to test, while stateful components are more powerful and flexible

• Example: Stateless component - const Button...read more
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Q4. What is reconciliation in ReactJS?
Ans. 
Reconciliation in ReactJS is the process of updating the DOM to match the virtual DOM after a component's state or props have changed.
• Reconciliation is the algorithm React uses to update the DOM efficiently.

• It compares the virtual DOM with the actual DOM and only updates the parts that have changed.

• Reconciliation is a key feature that helps React achieve high performance.

• Example: When a component's state changes, React...read more
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Q5. How is state changed in Redux?
Ans. 
State in Redux is changed by dispatching actions to reducers, which then update the state immutably.
• State changes in Redux by dispatching actions to reducers

• Reducers receive the current state and an action, then return a new state

• State is updated immutably in Redux
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Q6. What is the Combine Reducer in Redux?
Ans. 
Combine Reducer is a function in Redux that combines multiple reducers into a single reducer function.
• Combines multiple reducers into a single reducer function

• Helps manage different pieces of state in Redux store

• Improves code organization and maintainability

• Example: combineReducers({ reducer1, reducer2 })

• Example: const rootReducer = combineReducers({ reducer1, reducer2 })
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Q7. How is Relay different from Redux?
Ans. 
Relay is a GraphQL client specifically designed for React, while Redux is a state management library for any JavaScript app.
• Relay is tightly integrated with GraphQL, providing a declarative way to fetch and manage data for React components.

• Redux is a standalone state management library that can be used with any JavaScript framework, not just React.

• Relay encourages colocating data requirements with React components, whi...read more
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Q8. How can we structure the top-level directories in Redux?
Ans. 
Top-level directories in Redux should be structured based on functionality and feature modules.
• Organize directories based on feature modules, such as 'auth', 'todos', 'users'.

• Separate concerns by having directories for actions, reducers, components, and containers.

• Utilize a 'shared' directory for common functionality used across multiple feature modules.

• Consider using a 'utils' directory for utility functions and helpe...read more
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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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