Persistent Systems Senior Software Engineer Interview Questions, Process, and Tips

Q1. What is Difference between let var const,
Ans. 
let, var, and const are all used to declare variables in JavaScript, but they have different scoping rules and behaviors.
• let and const were introduced in ES6, while var has been around since the beginning of JavaScript.

• let and const are block-scoped, while var is function-scoped.

• Variables declared with const cannot be reassigned, while let and var can be.

• const variables must be initialized when they are declared, while...read more
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Q2. Sql and Mongo related questions such as fetch 3rd highest salary from employee table?
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Q3. What are the scope in javascript, describe each one.
Ans. 
Scopes in JavaScript determine the accessibility of variables and functions.
• Global scope: variables and functions declared outside any function are accessible globally

• Local scope: variables and functions declared inside a function are only accessible within that function

• Block scope: variables declared with let and const are only accessible within the block they are declared in

• Function scope: variables declared with var...read more
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Q4. What is callback hell, what is Promises?
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Callback hell is a situation where nested callbacks make code unreadable. Promises are a solution to this problem.
• Callback hell occurs when there are too many nested callbacks in asynchronous code

• It makes the code difficult to read and maintain

• Promises are a way to handle asynchronous operations without nested callbacks

• Promises can be used to chain multiple asynchronous operations together

• Promises have a resolve and re...read more
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Q5. What is express js and why it is used in web apps and what is body parser
Ans. 
Express.js is a popular Node.js web framework used for building web applications. Body-parser is a middleware used to parse incoming request bodies.
• Express.js is a minimal and flexible Node.js web application framework that provides a robust set of features for web and mobile applications.

• It provides a way to handle HTTP requests and responses, routing, middleware, and more.

• Body-parser is a middleware used to parse inc...read more
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Q6. What are arrow functions
Ans. 
Arrow functions are a concise way to write functions in JavaScript.
• They have a shorter syntax than traditional function expressions.

• They do not have their own 'this' keyword.

• They are not suitable for methods, constructors, or prototype methods.

• Example: const add = (a, b) => a + b;

• Example: const square = x => x * x;
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Q7. What is nodejs and difference between nodejs and javascript
Ans. 
Node.js is a server-side JavaScript runtime environment.
• Node.js is built on top of the V8 JavaScript engine from Google Chrome.

• It allows developers to write server-side code in JavaScript.

• Node.js has a non-blocking I/O model, making it efficient for handling large amounts of data.

• Node.js has a vast library of modules available through npm (Node Package Manager).
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Q8. What is passport.js why it is used
Ans. 
Passport.js is an authentication middleware for Node.js.
• Passport.js provides a simple way to authenticate users with various authentication strategies such as local, OAuth, OpenID, etc.

• It is highly customizable and can be integrated with any Node.js web application framework.

• Passport.js maintains user sessions and provides a consistent API for authentication across different strategies.

• Example: Using Passport.js with E...read more
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Q9. Difference between node and expressjs
Ans. 
Node is a runtime environment for executing JavaScript code, while Express is a web application framework built on top of Node.
• Node provides the platform for running JavaScript code outside of a web browser

• Express is a lightweight framework that simplifies building web applications on top of Node

• Express provides features like routing, middleware, and templating that make it easier to build web applications

• Node and Expr...read more
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Q10. Why nodejs is single Threaded
Ans. 
Node.js is single-threaded to optimize performance and simplify programming.
• Node.js uses an event-driven, non-blocking I/O model.

• This allows for efficient handling of multiple requests without creating new threads.

• Node.js also uses a single event loop to manage all I/O operations.

• This simplifies programming by eliminating the need for complex thread synchronization.

• However, Node.js can still take advantage of multi-cor
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Q1. A small data structures problem was given to solve
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Q2. A small web api asked to build which includes crud operations
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Q3. Question related to system design
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Q4. What is Function hoisting
Ans. 
Function hoisting is a JavaScript behavior where function declarations are moved to the top of their scope.
• Function declarations are moved to the top of their scope during the compilation phase.

• Function expressions are not hoisted.

• Hoisting can lead to unexpected behavior and bugs if not understood properly.
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Q5. What is event loops and phases
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Event loop is a mechanism that allows JavaScript to perform non-blocking I/O operations.
• Event loop is a loop that constantly checks the message queue and executes the next message if there is any.

• Phases are the different stages of the event loop, such as timers, I/O callbacks, idle, and poll.

• Event loop is crucial for Node.js to handle multiple requests simultaneously without blocking the main thread.

• Example: setTimeout...read more
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Coding test was mainly based on some easy level leetcode questions

Q1. Technical was sql quesries , few questions around linkedlist, few around graphs and trees
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Verbal, qunt, english etc..

Basic coding questions

It was very good and technical questions was basic.

Q1. What us sdlc? Use of it.
Ans. 
SDLC stands for Software Development Life Cycle. It is a process used by software development teams to design, develop, and test high-quality software.
• SDLC involves planning, designing, coding, testing, and deployment stages.

• It helps in ensuring that the software meets the requirements and is delivered on time and within budget.

• Examples of SDLC models include Waterfall, Agile, and DevOps.

• Each stage of SDLC has specific
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Q2. What is oops? Pilars or oops.
Ans. 
OOPs stands for Object-Oriented Programming. It is based on four main principles: Inheritance, Encapsulation, Abstraction, and Polymorphism.
• OOPs is a programming paradigm that focuses on objects and classes.

• The four main pillars of OOPs are Inheritance, Encapsulation, Abstraction, and Polymorphism.

• Inheritance allows a class to inherit properties and behavior from another class.

• Encapsulation refers to the bundling of da...read more
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