Infogain Reactjs Developer Interview Questions and Answers

Q1. React VirtualDOM
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Q2. ReactJS questions
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Q3. Inline vs block
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Inline elements flow in the same line, while block elements take up the full width available.
• Inline elements do not start on a new line and only take up as much width as necessary.

• Block elements start on a new line and take up the full width available.

• Examples of inline elements include <span>, <a>, and <strong>.

• Examples of block elements include <div>, <p>, and <h1>.
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Q1. What is hosting and closer
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Hosting is the process of storing a website or application on a server, while closure is a function that retains access to variables from its parent scope.
• Hosting involves storing a website or application on a server to make it accessible on the internet.

• Closure is a function that retains access to variables from its parent scope, even after the parent function has finished executing.
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Q2. What is difference between var let and const give me an explanation on what block scope
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var, let, and const are used to declare variables in JavaScript. var has function scope, let has block scope, and const is a constant with block scope.
• var has function scope, meaning it is accessible throughout the function it is declared in.

• let has block scope, meaning it is only accessible within the block it is declared in.

• const is similar to let in terms of block scope, but the value cannot be reassigned.
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Q3. What is asynchronous and how it works
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Asynchronous programming allows tasks to run independently of the main program flow, improving performance and responsiveness.
• Asynchronous code does not block the main thread, allowing other tasks to continue while waiting for a response.

• Callbacks, promises, and async/await are common ways to handle asynchronous operations in JavaScript.

• Example: fetching data from an API while the rest of the application continues to r
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Q4. Tell me the output 1)a = 20; console.log(a); var a; 2)b=10; console.log(b); let b; 3)let a =5; if(a<5){ let b = " a lessthen 5"; }else{ let b = "b is grater then 5"; } console.log(b);
Ans. 
The output for the given code snippets will be: 1) 20 2) ReferenceError: Cannot access 'b' before initialization 3) ReferenceError: b is not defined
• In the first snippet, variable 'a' is declared using 'var' after it is assigned a value, so it logs 20 without any issues.

• In the second snippet, variable 'b' is declared using 'let' after it is assigned a value, so it throws a ReferenceError as 'b' is accessed before initia...read more
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Q5. Give a div with text and display center of the page and apply animation using HTML and css
Ans. 
Use HTML and CSS to center a div with text and apply animation
• Create a div element with text inside

• Apply CSS to center the div on the page using flexbox or margin auto

• Use CSS animations like keyframes to add animation effects
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Q6. What are semantic tags and explain
Ans. 
Semantic tags are HTML tags that provide meaning to the content they enclose, helping search engines and screen readers understand the structure of a webpage.
• Semantic tags help improve SEO by providing context to search engines.

• They also improve accessibility for screen readers by clearly defining the structure of a webpage.

• Examples of semantic tags include

  ,
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Q7. How can we write responsive for web page
Ans. 
Use media queries, flexible grids, and relative units to create a responsive web page.
• Use media queries to apply different styles based on screen size

• Create flexible grids using CSS Grid or Flexbox

• Use relative units like percentages or ems for sizing elements

• Consider using frameworks like Bootstrap or Material-UI for responsive design

• Test your design on different devices and screen sizes
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Q8. What is the difference between CSS and SASS? what is the use of Sass
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SASS is a preprocessor scripting language that is interpreted into CSS, offering more features and flexibility.
• SASS is a preprocessor for CSS, allowing for variables, nesting, and mixins to be used in stylesheets.

• SASS code needs to be compiled into CSS before being used in a web project.

• SASS helps in writing cleaner and more organized CSS code, making it easier to maintain and update styles.

• CSS is the styling language ...read more
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Q9. Event propagation
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Q10. How would you validate the form using HTML? How do you validate the phone number with the country code?
Ans. 
Form validation using HTML and validating phone number with country code
• Use HTML5 form validation attributes like 'required', 'pattern', 'minlength', etc.

• For phone number validation, use 'pattern' attribute with regex for specific country code format

• Example: <input type='tel' pattern='[0-9]{3}-[0-9]{3}-[0-9]{4}' required>
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Q11. Which test library you use why it usecase
Ans. 
I use Jest for testing React applications due to its simplicity and integration with React ecosystem.
• Jest is the most popular test library for React applications

• It comes pre-configured with Create React App and has great support for snapshot testing

• Jest also has built-in mocking capabilities which make it easy to test components with dependencies
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Q12. Tell me mounting and shallow concept in testing library
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Mounting is the process of rendering a component into the DOM, while shallow rendering allows testing a component without rendering its children.
• Mounting is the initial phase of the component lifecycle where the component is rendered into the DOM.

• Shallow rendering in testing library renders only the component itself, not its children.

• Shallow rendering is useful for isolating the component being tested and avoiding rend...read more
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Q13. What is redux-toolkit and what difference b/w redux and redux-toolkit
Ans. 
Redux Toolkit is the official, recommended way to write Redux logic. It simplifies the process of managing state in React applications.
• Redux Toolkit provides a set of tools and best practices to streamline Redux development.

• It includes utilities like createSlice, createReducer, and configureStore to simplify the code and reduce boilerplate.

• Redux Toolkit also includes built-in Immer integration for writing immutable upd...read more
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Q14. How api call handle in redux and how can you get and display user name from redux
Ans. 
API calls in Redux are typically handled using middleware like Redux Thunk. User name can be retrieved from Redux state and displayed in components.
• Use Redux Thunk middleware to make API calls in Redux

• Dispatch actions to update Redux state with API response data

• Access user name from Redux state in components to display it
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Q15. React hooks and how optimization
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Q16. Why we need thank in redux
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Thunk middleware in Redux allows for asynchronous logic to be handled in Redux actions.
• Thunk middleware allows for dispatching functions instead of just plain objects in Redux actions.

• It enables handling asynchronous API calls within Redux actions.

• Thunk middleware helps in simplifying the code by moving complex logic outside of components.

• Example: Thunk middleware can be used to dispatch an action after a delay or to f...read more
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Q1. Basic Javascript Questions
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Q2. JS Array Questions
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Q1. Basic question from React JS, Redux, Javascript, HTML and CSS.
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Q2. Core concept like difference between virtual dom and real dom.
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Q3. What is Redux and flow of Redux. Difference between context api and Redux.
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Q1. Project related questions like what had you done in previous project.
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Q2. Some scenarios based questions.
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Q1. General HR questions.
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Q1. Alternative way for prop drilling
Ans. 
Context API or Redux can be used as alternative ways for prop drilling in React.
• Use Context API to pass data down the component tree without having to manually pass props at every level.

• Implement Redux to manage global state and access data from any component without prop drilling.

• Consider using React's useContext hook with Context API for a simpler way to consume context in functional components.
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Q1. Asked four programs
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Q1. Salary discussion
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Q1. Questions related to Current Job Profile and previous experience
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Q1. Basic of react.js and css
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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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