Infosys Reactjs Developer Interview Questions, Process, and Tips

Q1. All js concepts.
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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?
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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?
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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
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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
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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. What is the concept of redeclaration in JavaScript?
Ans. 
Redeclaration in JavaScript refers to the act of declaring a variable or function multiple times within the same scope.
• Redeclaring a variable using the 'var' keyword will not throw an error but will simply update the value of the variable.

• Redeclaring a variable using the 'let' or 'const' keyword within the same scope will result in a syntax error.

• Redeclaring a function within the same scope will override the previous f
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Q2. What are Promises?
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Promises in JavaScript are objects representing the eventual completion or failure of an asynchronous operation.
• Promises are used to handle asynchronous operations in JavaScript.

• They can be in one of three states: pending, fulfilled, or rejected.

• Promises can be chained using .then() to handle success and .catch() to handle errors.

• Example: const myPromise = new Promise((resolve, reject) => { ... });
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Q1. What is conditional rendering in React? What are closures? OOPS concept in JavaScript. What is ACID in database? Stack vs Heap
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Conditional rendering in React allows components to render different elements or components based on certain conditions.
• Conditional rendering is achieved using JavaScript expressions inside JSX.

• Common conditional rendering techniques include using if statements, ternary operators, and logical && operator.

• Example: rendering a component only if a certain condition is met - {condition ? : null}
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Q2. In react you can conditionally render component like when and which component to render by using if condition and other.
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Q1. Difference between var and let, difference between redux and flux
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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 is hoisting in JS
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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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Presentation components are class components that handle rendering, while functional components are simpler and handle stateless rendering.
• Presentation components are also known as container components.

• Functional components are also known as stateless components.

• Presentation components are used for complex UI logic and state management.

• Functional components are used for simple UI logic and stateless rendering.

• Functiona...read more
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Q6. Bind(), call(), apply() in JS
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