EPAM Systems React Js Frontend Developer Interview Questions and Answers

Q1. What projects or technologies I'm interested in?
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Q2. How I describe my seniority ?
Ans. 
I consider myself a mid-level React JS developer with a solid understanding of core concepts and practical experience in building applications.
• Experience with React hooks and state management libraries like Redux.

• Built responsive web applications using React, improving user engagement by 30%.

• Collaborated with cross-functional teams to deliver projects on time.

• Mentored junior developers, helping them understand React be...read more
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Q3. What was the most important work experience for you and why?
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Q1. How can we adapt the frontend to different view of devices?
Ans. 
Responsive design using media queries and flexible layouts to adapt frontend to different devices.
• Use media queries in CSS to apply different styles based on screen size

• Utilize responsive frameworks like Bootstrap or Foundation for pre-built responsive components

• Implement flexible layouts using percentage-based widths and max-width properties

• Optimize images for different screen resolutions using srcset and sizes attrib...read more
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Q2. What is a closure in Javascript?
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A closure is a function that has access to its own scope, as well as the outer scope in which it was defined.
• A closure allows a function to access variables from an outer function even after the outer function has finished executing.

• Closures are commonly used to create private variables and functions in JavaScript.

• Example: function outerFunction() { let outerVar = 'I am outer'; return function innerFunction() { console...read more
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Q3. What are the advantages of using Typescript? mention your favorite features
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Typescript offers advantages like static typing, improved code quality, better tooling support, and easier refactoring.
• Static typing helps catch errors at compile time

• Improved code quality due to type checking

• Better tooling support with features like code navigation and auto-completion

• Easier refactoring with the help of type annotations

• Faster development with enhanced IDE support
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Q4. Can you describe some Architectural Patterns ?
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Architectural patterns are reusable solutions to common problems in software architecture.
• MVC (Model-View-Controller) - Separates an application into three main components: the model, the view, and the controller.

• MVVM (Model-View-ViewModel) - Similar to MVC but with a ViewModel layer that manages the state and behavior of the view.

• Flux - Unidirectional data flow pattern commonly used with React applications.

• Microservic...read more
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Q5. Can you describe some Design Patterns ?
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Design patterns are reusable solutions to common problems in software design.
• Creational Patterns: Singleton, Factory, Builder

• Structural Patterns: Adapter, Decorator, Facade

• Behavioral Patterns: Observer, Strategy, Command
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Q6. Do you configured some part of a CI/CD pipeline?
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Yes, I have configured various parts of CI/CD pipelines.
• I have set up automated builds using tools like Jenkins or GitLab CI.

• I have configured automated testing processes within the pipeline.

• I have integrated deployment scripts to automatically deploy code to different environments.

• I have set up notifications for build status and deployment success/failure.

• I have worked on optimizing and improving the efficiency of CI/...read more
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Q7. Can you mention some popular hacker attacks?(xxs, sql injection, etc)
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Some popular hacker attacks include XSS (Cross-Site Scripting) and SQL Injection.
• XSS (Cross-Site Scripting) - attackers inject malicious scripts into web pages viewed by other users

• SQL Injection - attackers insert malicious SQL code into input fields to manipulate database queries
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Q8. Solve a React problem, the goal is not trigger re-renders of a siblings components from a parent node, but avoiding the memo, useMemo, or useCallback react utilities. You can modify the original structure
Ans. 
Optimize React component rendering by restructuring state management to prevent sibling re-renders.
• Use local state in child components instead of lifting state up to the parent.

• Implement context API for shared state without causing sibling re-renders.

• Utilize refs to manage mutable state that doesn't trigger re-renders.

• Consider using a state management library (like Redux) to isolate state changes.
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Q9. Describe the benefits of using SSR (server side rendering)
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SSR improves SEO, performance, and initial load time of web applications.
• Improves SEO by serving fully rendered HTML to search engine crawlers

• Enhances performance by reducing time to first paint and time to interactive

• Faster initial load time for users, especially on slower network connections

• Better support for social media crawlers and web scrapers

• Enables content to be visible to users even if JavaScript is disabled
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Q10. How can we fetch our data ? (fetch api, axios, forms, websockets, graphql, trpc, etc)
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Q11. Name performance techniques. It's a wide topic so prepared to explain in detail
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Q12. Do you know how to measure web performance? (lighthouse with it's scores measures)
Ans. 
Web performance can be measured using tools like Lighthouse, which provides scores on various metrics affecting user experience.
• Lighthouse evaluates performance based on metrics like First Contentful Paint (FCP) and Time to Interactive (TTI).

• A score of 90+ is considered good, while below 50 indicates poor performance.

• Lighthouse also assesses accessibility, SEO, and best practices, providing a holistic view of web perfo...read more
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Q13. Resolve a Leetcode problem -Merge two intervals.
Ans. 
Merge two intervals by sorting and iterating through the intervals.
• Sort the intervals based on the start value.

• Iterate through the intervals and merge overlapping intervals.

• Return the merged intervals.
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Q1. Difference between defer and async
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defer loads the script after the document has been parsed, async loads the script asynchronously without blocking the document parsing
• defer attribute loads the script after the document has been parsed

• async attribute loads the script asynchronously without blocking the document parsing

• defer scripts are executed in the order they appear in the document, async scripts are executed as soon as they are loaded

• defer is bette...read more
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Q2. Pseudo class vs Pseudo element
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Pseudo class selects elements based on their state, while pseudo element selects parts of an element.
• Pseudo class is used to style elements based on their state, such as :hover, :active, :focus.

• Pseudo element is used to style specific parts of an element, such as ::before, ::after, ::first-line.

• Pseudo class starts with a single colon (:), while pseudo element starts with a double colon (::).
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Q1. What is your method for preparing rice?
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I rinse the rice, cook it in a rice cooker with water and a pinch of salt, and let it steam for 20 minutes.
• Rinse the rice under cold water until the water runs clear to remove excess starch.

• Use a rice cooker with the appropriate water to rice ratio (usually 1:1 or 1:2 depending on the type of rice).

• Add a pinch of salt for flavor before starting the cooking process.

• Let the rice steam for about 20 minutes after it's done...read more
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Write a function , which accept a sorted array, and count the unique value in array. There can be negative number in array.eg arr[,-2, -1, -1, 0, 1,1 , 2, 3,3 , 4, 5]