Xcelore Interview Questions, Process, and Tips

Q1. NodeJS Event Loop in Depth
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Q2. Explain about API Security
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Q3. Explain Middlewares in NodeJS Express
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Q4. Database aggregations, indexing, optimization related questions
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Q5. Basic SQl queries
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Q6. Object Oriented Programming Basic Concepts
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Q1. What is Hoisting?
Ans. 
Hoisting is a JavaScript mechanism where variable and function declarations are moved to the top of their containing scope during compilation.
• Variable and function declarations are hoisted to the top of their scope.

• Only declarations are hoisted, not initializations.

• Function declarations take precedence over variable declarations.

• Hoisting can lead to unexpected behavior if not understood properly.
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Q2. What is Closures?
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Closures are functions that have access to variables from their containing scope even after the parent function has finished executing.
• Closures allow functions to maintain access to variables from their outer scope

• They are created when a function is defined within another function

• Closures are commonly used in event handlers and callbacks
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Q3. What is Promises?
Ans. 
Promises are a way to handle asynchronous operations in JavaScript, providing a cleaner alternative to callbacks.
• Promises represent the eventual completion (or failure) of an asynchronous operation.

• They allow you to chain multiple asynchronous operations together.

• Promises have states: pending, fulfilled, or rejected.

• You can handle the result of a promise using .then() and .catch() methods.

• Example: const myPromise = new
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Q4. What is Callback Hell?
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Callback Hell is a situation in asynchronous programming where multiple nested callbacks make the code hard to read and maintain.
• Occurs when multiple asynchronous operations are nested within each other

• Leads to deeply nested code which is hard to read and maintain

• Can be avoided by using Promises or async/await syntax
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Q5. What is Async/Await ?
Ans. 
Async/Await is a feature in JavaScript that allows for asynchronous programming using promises.
• Async/Await is syntactic sugar built on top of promises in JavaScript.

• It allows for writing asynchronous code that looks synchronous, making it easier to read and maintain.

• Async functions return a promise, which allows for chaining multiple asynchronous operations.

• Await keyword is used inside async functions to wait for a pro...read more
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Q1. Code A Todo List in React ?
Ans. 
A simple Todo List app built using React
• Create a new React project using create-react-app

• Create a Todo component to display the list of todos

• Use state to manage the list of todos and input field for adding new todos

• Implement functionality to add, delete, and mark todos as completed
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Q2. Difference Between RestApi and Graphql ?
Ans. 
REST API is a standard protocol for web services using HTTP, while GraphQL is a query language for APIs.
• REST API follows a client-server architecture with stateless communication, while GraphQL allows clients to request only the data they need.

• REST API typically uses multiple endpoints for different resources, while GraphQL uses a single endpoint for flexible data retrieval.

• REST API has predefined data structures, whil...read more
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Admin panel using mern stack to make

Q1. What is cors middleware?
Ans. 
CORS middleware is used to enable Cross-Origin Resource Sharing in web applications.
• CORS middleware allows servers to specify who can access their resources

• It adds necessary headers to HTTP responses to allow cross-origin requests

• Common CORS middleware libraries include 'cors' in Node.js and 'django-cors-headers' in Django
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Q2. What is event loop in javascript?
Ans. 
Event loop in JavaScript is a mechanism that allows asynchronous non-blocking code execution.
• Event loop is responsible for handling asynchronous operations in JavaScript.

• It continuously checks the call stack and the callback queue to see if there are any functions that need to be executed.

• Event loop ensures that JavaScript remains single-threaded and non-blocking.

• Example: setTimeout() function in JavaScript uses the ev...read more
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Q1. Java Core Questions like :- What is JVM What is Polymorphism, Types, Define their type with example What features Java you use and why? What is Collection? Do know about Streams, Lambdas? Difference betwee...read more
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