Ascentio Technologies S A Reactjs Developer Interview Questions and Answers

Q1. What is closure in javascript?
Ans. 
Closure is a feature in JavaScript that allows a function to access variables in its outer scope.
• A closure is created when a function is defined inside another function.

• The inner function has access to the outer function's variables and parameters.

• The outer function's variables and parameters are not accessible from outside the closure.

• Closures can be used to create private variables and methods.

• Example: function outer...read more
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Q2. What are ES6 features?
Ans. 
ES6 features are new additions to JavaScript language syntax and functionality.
• Arrow functions

• Template literals

• Let and const keywords

• Destructuring assignment

• Spread and rest operators

• Classes

• Modules

• Promises

• Default parameters

• Object.assign()

• Symbol data type
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Q1. What do you mean by redux and how to use redux
Ans. 
Redux is a predictable state container for JavaScript apps. It helps manage the state of an application in a more organized way.
• Redux is a state management tool commonly used with React to manage the state of an application.

• It follows a unidirectional data flow, where the state is stored in a single store.

• Actions are dispatched to update the state, and reducers specify how the state should change in response to actions...read more
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Q2. What is the use of Context Api in React
Ans. 
Context API is used in React to pass data through the component tree without having to pass props down manually at every level.
• Avoids prop drilling by providing a way to share values like themes, user data, etc. across the component tree.

• Helps in managing global state in React applications.

• Context API consists of Provider and Consumer components to provide and consume the context data.

• Can be used for theming, localizat
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Q1. What are the benefits of React?
Ans. 
React offers a component-based architecture, virtual DOM for performance optimization, and a strong community support.
• Component-based architecture allows for reusability and easier maintenance of code.

• Virtual DOM helps in improving performance by only updating the necessary parts of the actual DOM.

• React has a strong community support with a vast ecosystem of libraries and tools available.

• React allows for server-side re...read more
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Q2. Difference between state and props?
Ans. 
State is mutable and managed within the component, while props are immutable and passed from parent component.
• State is managed within the component and can be changed using setState() method

• Props are passed from parent component to child component and cannot be changed by the child component

• State is used for internal component data management, while props are used for passing data from parent to child components
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Q3. What is useReducer and UseContext api?
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useReducer is a React hook that manages state changes through a specified reducer function. useContext is a hook that allows access to a context object.
• useReducer is used for managing complex state logic in React applications.

• It takes in a reducer function and an initial state, and returns the current state and a dispatch function.

• Example: const [state, dispatch] = useReducer(reducer, initialState);

• useContext is used f...read more
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Q4. What is one way data binding?
Ans. 
One way data binding is a unidirectional flow of data from the model to the view in React applications.
• Data flows from the model (or source of truth) to the view, but not vice versa.

• Changes in the model automatically update the view, but changes in the view do not affect the model.

• Helps in maintaining a clear and predictable data flow in React components.
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Q5. Tell me hooks you have used?
Ans. 
I have used useState, useEffect, useContext, useReducer, and useRef hooks in my projects.
• useState - for managing state in functional components

• useEffect - for handling side effects in functional components

• useContext - for accessing context in functional components

• useReducer - for managing complex state logic in functional components

• useRef - for accessing DOM elements or storing mutable values
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Q6. What is redux middleware
Ans. 
Redux middleware is a function that intercepts actions before they reach the reducer.
• Middleware can be used for logging, crash reporting, asynchronous API calls, etc.

• It sits between the action dispatch and the reducer.

• Examples of popular middleware include redux-thunk and redux-saga.
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Q1. Questions related to Projects
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Q2. Git commands: How to commit ,merge code, how to resolve merge conflicts
Ans. 
Git commands for committing, merging code, and resolving merge conflicts
• To commit code: git commit -m 'Commit message'

• To merge code from a branch: git merge branch_name

• To resolve merge conflicts: manually edit the conflicting files, add changes, and then commit the merge
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It's 10 multiple-choice question with low,medium, and difficult range levels.

Q1. About CI-CD , JS browser working ,
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Q2. React basics like working and jsx
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Q1. What is closures, Hoisting with example Semantic elements
Ans. 
Closures and hoisting are important concepts in JavaScript.
• Closures refer to the ability of a function to access variables in its outer scope even after the function has returned.

• Hoisting is the behavior of moving variable and function declarations to the top of their respective scopes.

• Example of closures: function outer() { let x = 10; function inner() { console.log(x); } return inner; } const innerFunc = outer(); inn...read more
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Q2. Chaining Methods Currying Call bind and apply Optimization of application Server side rendering
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Q3. Selectors HTML 5 features
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Q1. Basics of react, javascript, hooks
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Q1. What is Pure components/memo/useCallback/HoC
Ans. 
Pure components, memo, useCallback, and HoC are optimization techniques in React for improving performance.
• Pure components are components that only re-render when their props or state change.

• memo is a higher order component that memoizes the result of a component rendering, preventing unnecessary re-renders.

• useCallback is a hook that memoizes functions, preventing unnecessary re-creations on re-renders.

• HoC (Higher Orde...read more
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