Holmium Technologies Node Js Backend Developer Interview Questions and Answers

Q1. What is Node Js
Ans. 
Node.js is a runtime environment that allows you to run JavaScript code outside of a web browser.
• Node.js is built on Chrome's V8 JavaScript engine.

• It uses an event-driven, non-blocking I/O model that makes it lightweight and efficient.

• Node.js is commonly used for building server-side applications and APIs.

• It has a large ecosystem of open-source libraries and frameworks, such as Express.js.
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Q2. What is middleware
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Middleware is a software component that acts as a bridge between an application's request and response.
• Middleware functions have access to the request and response objects

• They can modify the request and response objects

• Middleware can be used for tasks like authentication, logging, error handling, etc.
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Q3. What is promise
Ans. 
A promise is an object representing the eventual completion or failure of an asynchronous operation.
• Promises are used to handle asynchronous operations in JavaScript.

• They can be in one of three states: pending, fulfilled, or rejected.

• Promises can be chained using .then() to handle success and .catch() to handle errors.

• Example: new Promise((resolve, reject) => { setTimeout(() => resolve('Done!'), 1000); });
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Q4. What is promise.all
Ans. 
promise.all is a method in JavaScript that takes an array of promises and returns a single promise that resolves when all of the input promises have resolved.
• Used to handle multiple asynchronous operations at once

• Returns a single promise that resolves when all input promises have resolved

• If any of the input promises is rejected, the returned promise is rejected with the reason of the first rejected promise
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Q5. What is callback
Ans. 
A callback is a function passed as an argument to another function to be executed later.
• Callbacks are commonly used in asynchronous programming to handle tasks that take time to complete.

• They are often used in event handling, timers, and AJAX requests.

• Callbacks can be synchronous or asynchronous, depending on when they are executed.

• Example: setTimeout(callback, 1000) will execute the callback function after 1 second.
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Q1. What is closures? Problem of promise with settimeout
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Closures are functions that have access to variables from their outer scope, even after the outer function has finished executing.
• Closures are created when a function is defined inside another function.

• The inner function has access to the outer function's variables, even after the outer function has returned.

• Closures are useful for creating private variables and data encapsulation.

• They can be used to implement callback...read more
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BE AWARE THAT Interview starts at 10 ends at 6 in the evening

this will be 1st round

let arr=[{id:1,x:10},{id:2,y:10}}],let arr2=[{id:1:x10},{id:3,y:20}]
you need to combine both the object merge it into one

2. you will be given sql query to write that is get method

Q1. Can you provide a basic self-introduction?
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Q2. Which project you working right now and what are the challenges
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Array,Tree, Behaviour questions 2 hr duration easy-medium

Q1. Array Traversal using topological sort algorithm
Ans. 
Topological sort can be used to traverse an array of strings in a specific order.
• Topological sort is used to order elements based on their dependencies.

• In the context of array traversal, we can use topological sort to determine the order in which strings should be processed.

• For example, if strings represent tasks and their dependencies, we can use topological sort to ensure tasks are executed in the correct order.
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Q2. Right most node in almost complete bst
Ans. 
The rightmost node in an almost complete binary search tree is the last node in the last level of the tree.
• In an almost complete binary search tree, all levels are completely filled except possibly for the last level, which is filled from left to right.

• To find the rightmost node, start at the root and traverse the tree by always going to the right child until reaching the last level.

• The rightmost node will be the last
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Q1. Introduce yourself
Ans. 
I am a passionate Backend Developer with 5 years of experience in building scalable and efficient web applications.
• 5 years of experience in backend development

• Proficient in programming languages like Java, Python, and Node.js

• Strong understanding of database management systems such as MySQL and MongoDB

• Experience in developing RESTful APIs and microservices

• Familiar with cloud technologies like AWS and Azure
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Q2. Some python programs
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Q1. React questions
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Q2. Nodejs questions
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Q1. Find pairs from list whose is equals to target
Ans. 
Find pairs from list whose sum is equal to target
• Iterate through the list and for each element, check if the target minus the element exists in a hashmap

• If it exists, add the pair to the result list

• If it doesn't exist, add the current element to the hashmap
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Q2. Multiple iNheritance
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