CTS Consulting & Technical Support Reactjs Developer Interview Questions and Answers

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.

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.

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

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

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

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

  ,

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

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

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>

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

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

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

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

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

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>.

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

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.

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

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

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.