Mastek React Js Frontend Developer Interview Questions and Answers

React js state and useeffect

Duration was 1 hr and topics were css html react js vs code IDE it was a good experience

Q1. Basically javaacript concepts focused
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Q1. What is Observables?
Ans. 
Observables are a way to handle asynchronous data streams in Angular.
• Observables are similar to Promises, but can emit multiple values over time.

• They can be created using the RxJS library.

• They can be used for handling user input, HTTP requests, and other asynchronous operations.

• Operators can be used to transform, filter, and combine observables.

• Subscriptions are used to listen for emitted values and handle errors and c
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Q2. How to implement interfaces without methods?
Ans. 
Interfaces without methods can be implemented using type aliases.
• Type aliases can be used to define a shape of an object without any methods.

• Type aliases can be used to define a shape of an object with optional properties.

• Type aliases can be used to define a shape of an object with readonly properties.

• Type aliases can be used to define a shape of an object with union types.
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Q1. Why do you want to leave current company?
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Started with a normal assignment. A basic form application with few operation

Q1. Javascript basics and React native
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Q2. Closures,let var and const
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Q3. Threads of javascript, Architecture
Ans. 
Threads of javascript refer to the concept of asynchronous programming in JavaScript. Architecture in this context likely refers to the overall structure and organization of a React Native application.
• JavaScript is single-threaded, meaning it can only execute one piece of code at a time. Asynchronous programming allows for non-blocking operations, improving performance and user experience.

• React Native architecture typi...read more
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Q4. Storage, Secure storage, Offline app handling
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Q5. Push notification, Camera, geomaps
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Q1. Objective javascript questions
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Q1. Delete duplicate element from array
Ans. 
Remove duplicate elements from an array of strings
• Create a new Set from the array to remove duplicates

• Convert the Set back to an array using the spread operator

• Alternatively, use filter() and indexOf() to remove duplicates
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Q1. About you family etc.
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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 declarations are hoisted but not their initializations.

• 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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Q2. Name the CSS positions
Ans. 
CSS positions include static, relative, absolute, fixed, and sticky.
• Static - default position, elements are positioned according to the normal flow of the document

• Relative - positioned relative to its normal position

• Absolute - positioned relative to the nearest positioned ancestor

• Fixed - positioned relative to the viewport

• Sticky - acts like a combination of relative and fixed positioning
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Q3. What are semantic tags
Ans. 
Semantic tags are HTML tags that clearly define the content they contain for better accessibility and SEO.
• Semantic tags provide meaning to the content they enclose, making it easier for search engines to understand the structure of the page.

• Examples of semantic tags include

  ,

• Using semantic tags improves the accessibility of the website for users with disabilities, as screen readers can interp
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Q4. What is promise chaining
Ans. 
Promise chaining is a technique in JavaScript where multiple asynchronous operations are chained together to execute sequentially.
• Allows for handling multiple asynchronous operations in a more readable and organized way

• Each promise in the chain returns a new promise, allowing for further chaining

• Helps avoid callback hell by nesting promises inside each other

• Example: promise1.then(result => { return promise2; }).then(re
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Q5. Rest and spread operator
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Q6. What is virtual DOM
Ans. 
Virtual DOM is a lightweight copy of the actual DOM that React uses to improve performance by minimizing direct manipulation of the actual DOM.
• Virtual DOM is a concept in React where a lightweight copy of the actual DOM is created and updated in memory.

• When changes are made to the virtual DOM, React compares it with the actual DOM and only updates the necessary parts, reducing the number of direct manipulations to the ...read more
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Q7. Synthetic events in react
Ans. 
Synthetic events in React are events that are normalized by React to ensure consistent behavior across different browsers.
• Synthetic events are instances of the SyntheticEvent object in React.

• They are cross-browser compatible and have the same interface as native events.

• They are used to handle events like onClick, onChange, etc. in React components.

• Example: Click me
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Q8. What is redux in react
Ans. 
Redux is a predictable state container for JavaScript apps.
• Redux is a state management tool commonly used with React to manage the application's state in a predictable way.

• It helps in maintaining a single source of truth for the state of the entire application.

• Redux follows a unidirectional data flow, making it easier to understand how data changes over time.

• Actions are dispatched to update the state in Redux, and redu...read more
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Q9. What are hooks in react
Ans. 
Hooks in React are functions that let you use state and other React features without writing a class.
• Hooks were introduced in React 16.8.

• They allow you to use state and other React features in functional components.

• Some commonly used hooks are useState, useEffect, useContext, and useReducer.
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Q10. Difference between useMemo and useCallback
Ans. 
useMemo is used for memoizing values, while useCallback is used for memoizing functions.
• useMemo is used to memoize a value and only recompute it when its dependencies change.

• useCallback is used to memoize a function instance and only re-create it when its dependencies change.

• Example: useMemo can be used to memoize the result of a complex computation, while useCallback can be used to memoize a callback function passed t
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React js state and useeffect