1000+ Front end Developer Interview Questions and Answers

Data spooling is a process where data is temporarily stored in a buffer before being sent to an output device.

• Data spooling helps in managing the flow of data between different devices by storing it temporarily.

• It allows for efficient processing of data by decoupling the input/output operations.

• Examples of data spooling include print spooling, where print jobs are stored in a queue before being sent to the printer.

JavaScript is a versatile, high-level programming language primarily used for web development to create interactive and dynamic content.

• JavaScript is an interpreted, high-level language that supports object-oriented, imperative, and functional programming styles.

• It is dynamically typed, meaning variables can hold values of any type without explicit declaration (e.g., let x = 5; x = 'Hello';).

• JavaScript runs in the browser, allowing developers to create interactive web pages (...read more

React middlewares are functions that intercept and modify requests and responses in a React application.

• Middlewares are used to add additional functionality to an application without modifying the core code.

• They can be used for authentication, logging, error handling, and more.

• Examples of React middlewares include Redux Thunk, Redux Saga, and React Router.

• They are typically implemented using higher-order functions.

• Middlewares can be chained together to create a pipeline of fu...read more

Hoisting in JavaScript is a behavior where variable and function declarations are moved to the top of their containing scope during the compilation phase.

• Variable declarations are hoisted to the top of their scope, but not their assignments.

• Function declarations are fully hoisted, meaning they can be called before they are declared.

• Hoisting can lead to unexpected behavior if not understood properly.

Implement a dynamic form in React that renders input fields based on key-value pairs.

• Use React's state to manage form data dynamically.

• Map over the key-value pairs to create input fields and labels.

• Example: const formData = { name: 'John', age: 30 };

• Use controlled components to handle input changes.

• Example: <input value={formData.name} onChange={e => setFormData({...formData, name: e.target.value})} />

• Ensure the form updates automatically if the data changes.

Life cycle methods are methods that are automatically called at different stages of a component's life cycle in React.

• ComponentDidMount is called after the component has been rendered to the DOM.

• ComponentDidUpdate is called after the component's state or props have been updated.

• ComponentWillUnmount is called before the component is removed from the DOM.

Promises are objects representing the eventual completion or failure of an asynchronous operation.

• Promises have three states: pending, fulfilled, and rejected.

• Pending: initial state, neither fulfilled nor rejected.

• Fulfilled: operation completed successfully.

• Rejected: operation failed.

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

• Example: const promise = new Promise((resolve, reject) => { ... });

The 'this' operator refers to the object that is currently executing the code.

• The value of 'this' depends on how a function is called.

• In a method, 'this' refers to the object that owns the method.

• In a regular function, 'this' refers to the global object (window in a browser).

• In an event handler, 'this' refers to the element that received the event.

• The value of 'this' can be explicitly set using call(), apply(), or bind() methods.

display none removes element from layout, visibility hidden hides element but still takes up space

• display none removes the element from the layout completely

• visibility hidden hides the element but still takes up space

• display none will not render the element, while visibility hidden will render the element but make it invisible

Session storage is temporary and data is cleared when the browser is closed, while local storage persists even after the browser is closed.

• Session storage is temporary and data is cleared when the browser is closed

• Local storage persists even after the browser is closed

• Session storage is limited to the current tab or window, while local storage is shared across tabs and windows of the same origin

The CSS Box Model is a fundamental concept in CSS that defines the layout and spacing of elements on a webpage.

• The Box Model consists of content, padding, border, and margin.

• Content: The actual content of the box, such as text or images.

• Padding: Space between the content and the border.

• Border: The border surrounding the padding and content.

• Margin: Space outside the border, separating the element from other elements.

• Example: div { width: 200px; padding: 20px; border: 1px solid...read more

CSS Flexbox is a layout module that helps in creating flexible and responsive layouts.

• Flexbox is used to align and distribute space among items in a container.

• It has properties like display, flex-direction, justify-content, align-items, and flex-wrap.

• Flexbox is widely used in modern web development for creating responsive designs.

• Example: display: flex; flex-direction: row; justify-content: center; align-items: center;

Scss/Sass is a CSS preprocessor that adds features like variables, nesting, and mixins to make writing CSS easier and more efficient.

• Scss/Sass stands for Syntactically Awesome Style Sheets

• It is a CSS preprocessor that compiles into regular CSS

• It adds features like variables, nesting, and mixins to make writing CSS easier and more efficient

• It also allows for more advanced features like functions and loops

• Example: $primary-color: #007bff; .button { background-color: $primary-co...read more

Functional components are simpler and easier to test, while class components offer more features and lifecycle methods.

• Use functional components for simple UI components

• Use class components for more complex UI components

• Functional components are easier to read and maintain

• Class components offer more lifecycle methods and state management options

React.js is a JavaScript library used for building user interfaces by creating reusable UI components.

• React.js allows developers to create interactive user interfaces efficiently.

• It uses a virtual DOM for optimal performance by updating only the necessary components.

• React components can be reused across different parts of an application.

• It follows a unidirectional data flow, making it easier to manage state and data.

• React.js is maintained by Facebook and a community of develo...read more

Controlled components are React components whose value is controlled by React, while uncontrolled components are not.

• Controlled components are typically used for forms and inputs

• Uncontrolled components are typically used for simple inputs like text fields

• Controlled components use the 'value' prop to set the value of the component

• Uncontrolled components use the 'defaultValue' prop to set the initial value of the component

• Controlled components allow for more control and validat...read more

Dependency injection in Angular is a design pattern where components are given their dependencies rather than creating them themselves.

• In Angular, dependency injection is achieved by declaring the dependencies in the constructor of a component or service.

• It helps in making components more modular, reusable, and easier to test.

• For example, if a component needs a service to fetch data from an API, instead of creating an instance of the service within the component, the service ...read more

Position absolute is positioned relative to its closest positioned ancestor, while position relative is positioned relative to its normal position in the document flow.

• Position absolute elements are taken out of the normal document flow.

• Position relative elements are still in the normal document flow but can be moved from their original position using top, bottom, left, and right properties.

• Position fixed elements are positioned relative to the viewport and do not move when t...read more

To center 3 divs vertically and horizontally, use flexbox and align-items/justify-content properties.

• Wrap the 3 divs in a parent container

• Set the parent container's display property to flex

• Set the parent container's align-items and justify-content properties to center

Server-Side Rendering is rendering the web page on the server and sending the fully rendered page to the client, while Client-Side Rendering is rendering the web page on the client's browser using JavaScript.

• Server-Side Rendering generates the HTML on the server and sends it to the client, resulting in faster initial page load.

• Client-Side Rendering loads a basic HTML page first and then uses JavaScript to render the content on the client's browser, which can result in slower ...read more

Modernizing legacy systems and integrating new technologies in a global infrastructure.

• Identify key pain points in the legacy system that need modernization

• Develop a clear roadmap for integration of new technologies while minimizing disruption

• Collaborate with stakeholders to ensure alignment with business goals

• Implement gradual changes and conduct thorough testing to mitigate risks

• Provide training and support for users to adapt to the new technologies

A chat app db should have tables for users, conversations, messages, and attachments.

• Create a table for users with their unique ID, username, and password.

• Create a table for conversations with their unique ID, name, and participants.

• Create a table for messages with their unique ID, conversation ID, sender ID, and message content.

• Create a table for attachments with their unique ID, message ID, and attachment URL.

Event bubbling can be implemented by attaching event listeners to the child, parent, and grandparent divs.

• Add event listeners to the child, parent, and grandparent divs

• Use the event.stopPropagation() method to stop the event from bubbling up to the parent and grandparent divs

• Handle the event in each div's event listener function

Media elements in HTML are used to embed audio and video content on a webpage.

• Media elements include <audio> and <video> tags in HTML.

• They allow for the playback of audio and video files directly on a webpage.

• Attributes like src, controls, autoplay, and loop can be used to customize the behavior of media elements.

• Example: <video src='video.mp4' controls></video>

Count the number of words in given strings of array using higher order function.

• Use the map function to transform each string into an array of words

• Use the reduce function to count the total number of words in all strings

• Handle edge cases such as empty strings or strings with leading/trailing spaces

Yes, you can apply multiple colors to text using CSS with a single tag by utilizing techniques like gradients or text shadows.

• Use CSS gradients: `background: linear-gradient(to right, red, blue); -webkit-background-clip: text; color: transparent;`

• Apply text-shadow for a multi-colored effect: `text-shadow: 1px 1px red, 2px 2px blue;`

• Utilize the `mask-image` property for advanced color effects: `mask-image: linear-gradient(to right, red, blue);`

Lifecycle hooks in Angular are methods that allow you to tap into specific points in a component's lifecycle.

• Lifecycle hooks include ngOnInit, ngOnChanges, ngDoCheck, ngOnDestroy, etc.

• ngOnInit is used for initialization logic, ngOnChanges for reacting to input changes, ngDoCheck for custom change detection, ngOnDestroy for cleanup tasks, etc.