ITC Infotech Reactjs Developer Interview Questions and Answers

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
Ans. 
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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Q1. Difference between var and let, difference between redux and flux
Ans. 
Var is function scoped, let is block scoped. Redux is a predictable state container, Flux is an architecture pattern.
• Var can be redeclared and updated within its scope, let cannot be redeclared but can be updated within its scope

• Redux has a single store for the entire application, while Flux has multiple stores

• Redux uses a unidirectional data flow, while Flux uses a bidirectional data flow

• Redux has middleware for handl...read more
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Q2. Output based questions on var and let.
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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.

Q1. Basic Javascript, React Js question
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Q1. Basic Question JS , React JS , Redux
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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. Component lifecycle
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Q2. What is DOM tree?
Ans. 
DOM tree is a hierarchical representation of HTML elements in a web page.
• DOM stands for Document Object Model.

• It is a tree-like structure where each node represents an HTML element.

• The DOM tree is created by the browser when a web page is loaded.

• It allows JavaScript to manipulate the content, structure, and style of a web page.
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Q3. What is the difference between props and state?
Ans. 
Props are immutable and passed from parent component, while state is mutable and managed within the component.
• Props are read-only and cannot be modified by the component receiving them.

• State is mutable and can be changed by the component that owns it.

• Props are passed from parent to child components, while state is managed within the component itself.

• Example: Props can be used to pass data from a parent component to a c...read more
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Q4. What is redux and when to use it and when not to use it?
Ans. 
Redux is a predictable state container for JavaScript apps. It is used to manage application state in a centralized way.
• Use Redux when you have complex state management needs in your application.

• Redux is helpful for large applications with many components that need access to the same state.

• Avoid using Redux for simple applications with minimal state management requirements.

• Consider using React's built-in state manageme...read more
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Q5. Two arrays passed to one function, then remove the elements passed from source array and present in another array
Ans. 
Remove elements from source array present in another array passed to a function
• Loop through elements in source array and check if they exist in the other array

• If an element is found in both arrays, remove it from the source array
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Q1. What is DOM tree

Ans. 

DOM tree is a hierarchical representation of HTML elements in a web page.

• DOM stands for Document Object Model

• It is a tree-like structure where each node represents an HTML element

• The root node is the element, followed by and elements

• Nodes can have parent-child relationships, siblings, and descendants

• JavaScript can manipulate the DOM to dynamically update the content and structure of a web page

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