Infosys React Js Frontend Developer Interview Questions, Process, and Tips

Q1. What is closure
Ans. 
A closure is a function that has access to its own scope, as well as the scope in which it was defined.
• A closure allows a function to access variables from an outer function even after the outer function has finished executing.

• Closures are commonly used to create private variables in JavaScript.

• Example: function outerFunction() { let outerVar = 'I am outer'; return function innerFunction() { console.log(outerVar); }; }
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Q2. What is webworkers
Ans. 
Web Workers are a way to run JavaScript code in the background, separate from the main thread of the web application.
• Web Workers allow for multi-threading in JavaScript, improving performance by offloading tasks to separate threads.

• They can be used for tasks like heavy calculations, image processing, or other CPU-intensive operations.

• Communication between the main thread and Web Workers is done through message passing.

• ...read more
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Q3. What is first class function and
Ans. 
A first class function is a function that can be treated like any other variable in a programming language.
• Can be passed as an argument to other functions

• Can be returned from other functions

• Can be assigned to variables

• Can be stored in data structures
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Q4. What is first paint and temporal dead zone
Ans. 
First paint refers to the time when the browser starts rendering pixels to the screen. Temporal dead zone is a period in JavaScript where a variable exists but cannot be accessed.
• First paint is the time when the browser starts rendering content on the screen.

• Temporal dead zone is a period in JavaScript where a variable is declared but cannot be accessed due to the variable being in an inaccessible state.

• Example: const ...read more
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Q5. What is callback, event deligaton, react reconcillaton, react life cycle methods
Ans. 
Callbacks, event delegation, React reconciliation, and React lifecycle methods are key concepts in React development.
• Callback functions are functions passed as arguments to be executed later, commonly used in event handling and asynchronous operations.

• Event delegation is a technique where a single event listener is attached to a parent element to manage events for multiple child elements.

• React reconciliation is the pro...read more
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Q6. Implementing redux
Ans. 
Implementing Redux in a React application involves several steps to manage state globally.
• Install Redux and React-Redux libraries using npm or yarn.

• Create a Redux store to hold the state of the application.

• Define reducers to specify how the state should change in response to actions.

• Dispatch actions to update the state in the Redux store.

• Connect React components to the Redux store using the connect function from React-...read more
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Q1. Create a table component from array of objects
Ans. 
Create a table component from array of objects in React JS
• Map through the array of objects to render rows in the table

• Use Object.keys() to dynamically generate table headers

• Utilize CSS for styling the table
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Q2. What is event loop
Ans. 
Event loop is a mechanism in JavaScript that allows for asynchronous operations to be executed in a non-blocking way.
• Event loop is responsible for handling the execution of code in a single-threaded environment.

• It continuously checks the call stack for any functions that need to be executed.

• If the call stack is empty, it looks at the task queue for any pending tasks to be executed.

• Event loop ensures that JavaScript rem...read more
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Discussion about javascript concepts

Coding for react components

Q1. Difference between props and data
Ans. 
Props are used to pass data from parent to child components in React, while data refers to the information stored within a component.
• Props are read-only and cannot be modified by the child component.

• Data is mutable and can be changed within the component.

• Props are passed down from parent to child components, while data is stored within the component itself.

• Example: Passing a 'name' prop from a parent component to a chi...read more
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Q2. Lifecycle methods
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Q1. Describe your greatest Strength
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Q2. Describe your greatest Weakness
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50 minutes coding round they asked me some theoretical question and machine coding question they asked me DSA question

Mathematics question

Q1. What is react js
Ans. 
React JS is a JavaScript library for building user interfaces.
• React JS is a front-end library developed by Facebook.

• It allows developers to create interactive user interfaces.

• React uses a component-based architecture for building reusable UI components.

• It uses a virtual DOM for efficient rendering of UI components.

• React can be used to build single-page applications, mobile apps, and more.
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Q2. What is 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 useRef.

• Hooks help in reusing stateful logic across components.

• Example: useState hook is used to add state to a functional component.
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