Interview Questions

Question 1

What is React?

Answer 1

React is a popular JavaScript library for building user interfaces that allows developers to create interactive and dynamic web applications efficiently. It uses a component-based architecture to break down the UI into reusable, self-contained pieces.

Question 2

What is Redux?

Answer 2

Redux is a JavaScript library used for managing the state of a web application in a predictable and centralized manner. Its primary purpose is to help maintain and update the application’s data in a consistent way, making it easier to manage and debug complex applications.

Question 3

How does Redux work?

Answer 3

Redux manages the application’s state in a single store and manages the state with actions and reducers. Actions describe changes or events in-app while reducers specify how the state should modify based on the action. Components can subscribe to the store to receive the updated state, facilitating a structured data flow in the app.

Question 4

What makes Redux so special?

Answer 4

Redux is special because it provides a predictable and centralized way to manage an application’s state.

Question 5

Redux setup process?

Answer 5

install redux, create store, create reducers functions, create action objects, dispatch actions, connect components to store, subscribe components to store, optional middleware (redux-thunk), initialize state, and render components

Question 6

What are reducers in Redux?

Answer 6

In Redux, reducers are functions that specify how an application’s state should change in response to actions.

Question 7

Why do you choose React?

Answer 7

Because React is component-based, it promotes reusability and makes it easier to build complex applications. React uses the virtual DOM, optimizing rendering. Backed by a strong community and maintained by Facebook. React has a RIch ecosystem of 3rd party libraries (react-router, redux) that extend functionality.

Question 8

What is AJAX?

Answer 8

Asynchronous Javascript and XML, allow the web app to retrieve data in the background making web apps faster and seamless. Sending and receiving data without refreshing the whole page

Question 9

What is reponsive design?

Answer 9

creating websites that adapt to various screen-sized to ensure its user-friendly.

Question 10

What is the difference between REST and RESTful API?

Answer 10

REST is the architectural style, the set of guidelines, best practices, and constraints.

RESTful API is the actual implementation of that architectural style. It’s what developers create and consumers (like apps or other services) interact with over the web.

Question 11

what is a RESTful api?

Answer 11

A RESTful API is a web service that adheres to REST principles, using standard HTTP methods for clients to access and manipulate resources in a predictable way

RESTful APIs provide a standardized way to communicate with backend systems to create dynamic and interactive applications.

Question 12

what is the purpose of a RESTful API?

Answer 12

The purpose of using a RESTful API is to enable applications to exchange data over the Internet in a standardized manner,

Question 13

what is closure?

Answer 13

Closure is a function that retains access to variables in its outer scope even after the outer scop function has finished executing. This allows the inner function to “remember” those variables, providing a way to encapsulate data, often used for creating private variables and maintaining state within functions.

Question 14

What is a promise?

Answer 14

A Promise is an asynchronous value, a value that is unknown now but can be known in the future. its like saying “I’ll let you know when I am done, you can decide what to do later whether success or error”. this way better to load data preventing the whole app from freezing.

Question 15

What is a callback?

Answer 15

A function passed as a parameter to another function.

Question 16

What are the major features of React?

Answer 16

component based which are reusable components to build complex apps, virtual dom and reconciliation which updates only specific components not the entire app, React allows you to write in JSX, JS syntax that makes your code more readable, strong community behind it

Question 17

What is JSX?

Answer 17

JavaScript XML, a syntax extension used for Javasciprt used in React to describe how the UI should look like.. It is HTML-like code that makes it easier to create and render components in a readable manner. JSX later gets transformed into javascript with Babel.

Question 18

What is the Virtual DOM?

Answer 18

Virtual DOM is a blueprint of the actual DOM.

Question 19

How does the Virtual DOM work?

Answer 19

When something changes, the virtual DOM is updated first, then it compares the virtual DOM with the actual DOM, and changes only update the parts that are different.

Question 20

What is the difference between state and props?

Answer 20

Props are immutable, are used for parent-child communication, promote reusability and one-way data flow

State is mutable, managed internally, triggers reusability and is scoped to the component

Question 21

what is state?

Answer 21

State is the status and data store of a component at a specific point in time. It encompasses all the variables data and dictates how the component looks and behaves.

Question 22

What does lifting state up mean and why do we do it?

Answer 22

Lifting state refers to moving the state from child to parent component. By doing so you centralize the state management making it easier to coordinate interactions and data flow between sibling components

Question 23

Why do we set a key property when we map over an array in React?

Answer 23

The ‘key’ helps React know which elements have changed or need to be updated, optimizing the rendering process.

Question 24

what are the core principles of Redux?

Answer 24

The core principles of Redux are maintaining a single immutable state tree and an unidirectional data flow. Actions describe changes that are processed by reducers to update the state, which in turn re-renders the UI. Redux ensures a predictable and debuggable app.

Question 25

How do I make an AJAX request using Redux?

Answer 25

In Redux you usually make AJAX requests using middleware such as Redux Thunk. Within your action create you initialize the AJAX request and then dispatch actions to update the state based on the response.

Question 26

What are the benefits of using Redux DevTools?

Answer 26

Redux DevTools are useful for debugging as they can track the Redux store of an application.

Question 27

How do I use React DevTools? What does this help me with?

Answer 27

In React DevTools you can inspect the components state and props helping with the debugging process.

Question 28

What is closure and how is it used by React?

Answer 28

When there is a function inside another function then the inner function has access to the variables and scope of the outer function and its ancestors.

React uses closures to capture and remember the current state and props in functional components and hooks, like useState and useEffect. This enables better encapsulation and helps in maintaining state across re-renders, providing a more predictable behavior, especially in asynchronous operations.

Question 29

What is redux-thunk?

Answer 29

Redux-Thunk is a Redux middleware used for write action create that output functions instead of plain objects. This allows you to manage Asynchronous operations and dispatch different actions depending on the API calls.

Question 30

What is the difference and similarities between React context vs Redux?

Answer 30

Both are used to manage state. React context is built in React and Redux is a more structured and scalable architecture used to make more complex applications.

Question 31

What’s the benefit of using async/await?

Answer 31

Makes async/await code improve readability and improve error handling as try/catch blocks can be added.

Question 32

What is cookie? cookies vs localStorage vs sessionStorage?

Answer 32

Cookies, localStorage, and sessionStorage are web storage options that differ in accessibility, lifetime, and storage capacity. Cookies are accessible on both the server and client, have expiration settings, and are limited to 4KB, while localStorage and sessionStorage are client-side only, with localStorage being persistent and sessionStorage limited to a browser session, both offering around 5-10MB of storage

Question 33

What is prototypal inheritance?

Answer 33

Prototypal inheritance in Javascript allows objects to access other objects and functions based on the prototype chain.

Question 34

What is the DOM?

Answer 34

The Document Object Model (DOM) is a structured representation of an HTML or XML document, allowing you to manipulate its content and structure using JavaScript. its the bridge between HTML and JS.

Question 35

How to copy an Array?

Answer 35

[…array] or array.slice() –> both are shallow copies

Question 36

How to compare two objects?

Answer 36

Perform a shallow comparison by iterating through one of the objects comparing each key and value with the other object.

Question 37

What is asynchronous programming and why is it important in JavaScript?

Answer 37

Improves user experience by allowing you to perform JS operation in the background without interrupting the main thread of execution.

Question 38

What is hoisting?

Answer 38

In JS, Hoisting is moving the variable and function declaration to the top of the containing scope. This enables function and variable call before declaration.

Question 39

What is apply, call and bind?

Answer 39

Apply, Call and Bind, are used to set the “this” context on a function. Apply and call are invoked immediately and Bind is set for a predetermined this.

Question 40

DIfference between let, var, const

Answer 40

All these are for variable declarations. Var is function scope and is hoisted to undefined. While let and const are block scope and are not hoisted, Const doesn’t have reassignment property.

Question 41

What’s the difference between a variable that is: null, undefined or undeclared? How would you go about checking for any of these states?

Answer 41

null is an explicitly empty value set by the developer.
undefined means a variable has been declared but hasn’t been assigned a value yet.
Undeclared variables are those that have not been declared at all and trying to access them results in an error.

Question 42

what is higher order function?

Answer 42

Higher Order functions increase the maintainability and functionality of a function by allowing you to pass functions as other arguments.

Question 43

What is the difference between store and reducer

Answer 43

Store contains the entire state tree of an application, a reducer is a function that takes the current state and an action and is able to update the state based on the dispatched action.

Question 44

What is the difference between == and ===?

Answer 44

”==” does type coercion. meaning it makes both values the same type before comparing, while “===” check for both type and value.

Question 45

What are Agile Methodologies?

Answer 45

Agile is a flexible approach to project management and software development that emphasizes incremental delivery, collaboration, and adaptability to change.

Question 46

What is the Scrum Method?

Answer 46

Scrum is a framework within Agile that structures teamwork with specific roles, regular progress checks, and iterative product increments to deliver work efficiently.