CTS Consulting & Technical Support Reactjs Developer Interview Questions and Answers

Q1. What are the advantages of React
Ans. 
React offers advantages such as virtual DOM for improved performance, reusable components, and easy integration with other libraries.
• Virtual DOM for efficient updates and improved performance

• Reusable components for easier development and maintenance

• Easy integration with other libraries like Redux for state management

• Support for server-side rendering for better SEO performance
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Q2. How the performance optimization can be done in React Js Application
Ans. 
Performance optimization in React Js can be achieved through code splitting, memoization, virtualization, and minimizing re-renders.
• Implement code splitting to load only necessary components when needed

• Use memoization techniques like useMemo and useCallback to prevent unnecessary re-renders

• Implement virtualization for long lists or tables to render only visible items

• Minimize re-renders by using shouldComponentUpdate or
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Q3. What is the purpose of useMemo and UseCallBack hook
Ans. 
useMemo and useCallback are hooks in React used for optimizing performance by memoizing values and functions respectively.
• useMemo is used to memoize the result of a function so that it is only recomputed when its dependencies change.

• useCallback is used to memoize a function instance so that it is not recreated on every render unless its dependencies change.

• Both hooks help in optimizing performance by preventing unneces...read more
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Q1. Explain useSelector
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useSelector is a hook provided by React-Redux for accessing the Redux store state in functional components.
• Allows functional components to access the Redux store state without connecting to the store

• Accepts a selector function as an argument to specify which part of the state to extract

• Automatically subscribes to the Redux store updates and re-renders the component when the selected state changes
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Q2. Optimization in react
Ans. 
Optimization in React involves improving performance and efficiency of the application.
• Use shouldComponentUpdate or PureComponent to prevent unnecessary re-renders

• Avoid using inline functions in render method to prevent re-renders

• Use keys in lists to help React identify which items have changed

• Splitting components into smaller ones can improve performance

• Use React.memo for functional components to memoize the result
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Q3. What is JSX in react
Ans. 
JSX is a syntax extension for JavaScript used in React to write HTML-like code within JavaScript.
• JSX allows developers to write HTML-like code directly in their JavaScript files

• It makes the code more readable and easier to understand

• JSX gets transpiled into regular JavaScript by tools like Babel before being rendered by the browser
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Q4. Explain redux flow in react
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Redux flow in React involves actions, reducers, store, and components to manage state in a centralized manner.
• Actions are dispatched to describe what happened in the application.

• Reducers specify how the state changes in response to actions.

• Store holds the state of the application.

• Components can connect to the store to access and update the state.
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Q5. Stateful and stateless components
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Q1. Brief about project
Ans. 
Developed a web application for managing inventory and sales
• Used Reactjs for front-end development

• Implemented Redux for state management

• Integrated with backend APIs using Axios

• Designed responsive UI for better user experience
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Q2. Asked me about graph ql
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Q3. Asked topic on routing .
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Q1. Difference between if else and ternary
Ans. 
Ternary operator is a shorthand for if else statement in JavaScript.
• Ternary operator is written as condition ? expression1 : expression2

• If the condition is true, expression1 is executed, else expression2 is executed

• Ternary operator is more concise and can be used inline in JSX
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Q2. Class and functional components
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Q1. About my projects
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Q2. About strenghts and weeknesses
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Q1. About my experience
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Q2. Salary discussions
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Q1. Questions related to Current Job Profile and previous experience
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Q1. What is hoisting in JS
Ans. 
Hoisting is a JavaScript behavior where variable and function declarations are moved to the top of their containing scope.
• Hoisting applies to both variable and function declarations.

• Variable declarations are hoisted but not their initializations.

• Function declarations are fully hoisted, allowing them to be called before they are declared.

• Hoisting does not apply to variables declared with let or const.

• Hoisting can lead t...read more
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Q2. What are higher-order functions in JS
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Higher-order functions are functions that take one or more functions as arguments or return a function as their result.
• Higher-order functions can be used to create reusable code by abstracting common patterns.

• They enable functional programming paradigms like currying and composition.

• Examples of higher-order functions in JavaScript include map, filter, and reduce.
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Q3. Difference between var, let, and const in JS
Ans. 
var is function scoped, let and const are block scoped.
• var can be redeclared and updated within its scope

• let can be updated but not redeclared within its scope

• const cannot be updated or redeclared once declared

• let and const are not hoisted like var

• const must be initialized during declaration
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Q4. What are Hooks in React.js
Ans. 
Hooks are a feature in React.js that allow developers to use state and other React features in functional components.
• Hooks are functions that let you use React features in functional components

• They allow you to use state and other React features without writing a class

• Hooks provide a way to reuse stateful logic between components

• Some commonly used hooks are useState, useEffect, and useContext
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Q5. Presentation component vs functional component in React.js
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Q6. Bind(), call(), apply() in JS
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Progress bar in react and remote data fetching

Q1. Ui related questions
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Q1. Asked for preferred location and salary
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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?
Ans. 
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.