100+ Front end Developer Interview Questions and Answers for Freshers

The Document Object Model (DOM) is a programming interface for web documents. It represents the structure of a document as a tree of objects.

• DOM is a platform and language-neutral interface that allows programs and scripts to dynamically access and update the content, structure, and style of a document.

• It provides a structured representation of the document as a tree of objects, where each node represents a part of the document.

• DOM allows developers to manipulate the document...read more

let is block scoped while var is function scoped in JavaScript.

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

• var is function scoped, meaning it is accessible throughout the function it is declared in.

• Using let can help prevent variable hoisting issues.

• let allows you to redeclare a variable in the same scope, while var does not.

ES5 is the fifth version of ECMAScript, while ES6 is the sixth version. ES6 introduced new features and syntax improvements.

• ES5 is widely supported by all major browsers, while ES6 support is gradually increasing.

• ES6 introduced let and const for variable declarations, arrow functions, classes, and modules.

• ES6 also added new built-in methods like map, filter, and reduce for arrays.

• ES6 introduced template literals, destructuring assignment, and default function parameters.

JavaScript is a scripting language used for web development, while Java is a general-purpose programming language.

• JavaScript is primarily used for client-side scripting and web development.

• Java is a compiled language used for building applications that can run on any platform.

• JavaScript is dynamically typed, while Java is statically typed.

• JavaScript has a prototype-based object-oriented programming model, while Java has a class-based model.

• JavaScript is often embedded within ...read more

Async/await is a syntax for writing asynchronous code in a synchronous way.

• Async/await is built on top of Promises.

• Async functions always return a Promise.

• Await can only be used inside an async function.

• Async/await makes code easier to read and write compared to using callbacks or Promises.

Redux is a predictable state container for JavaScript apps. It helps manage the state of an application in a single immutable state tree.

• Redux is commonly used with React to manage the state of the application.

• It provides a centralized store for all the state in an application.

• Actions are dispatched to update the state in Redux.

• Reducers specify how the state changes in response to actions.

• Redux helps in maintaining a predictable state flow in the application.

• It simplifies the...read more

The web is a system of interconnected documents and resources accessed via the internet.

• The web is made up of websites, web pages, and web applications.

• It allows users to access information, communicate, and interact with others online.

• The web relies on protocols like HTTP and HTML to function.

• Examples include websites like Google, Facebook, and Wikipedia.

React JS is a JavaScript library for building user interfaces.

• React JS allows developers to create reusable UI components

• JSX is a syntax extension for JavaScript that allows developers to write HTML-like code in their JavaScript files

• Prop drilling is the process of passing props down through multiple levels of nested components in order to access them in a lower-level component

Virtual DOM is a lightweight copy of the actual DOM, used to improve performance and reduce unnecessary re-rendering of web pages.

• Virtual DOM updates only the necessary parts of the page, reducing the need for full page reloads.

• It allows for faster rendering and improved user experience.

• React is a popular library that uses Virtual DOM to manage updates efficiently.

MERN stack is a combination of MongoDB, Express.js, React.js, and Node.js used to build full-stack web applications.

• Start by setting up the backend with Node.js and Express.js

• Use MongoDB as the database to store and retrieve data

• Build the frontend using React.js to create interactive user interfaces

• Connect the frontend and backend using APIs

• Deploy the application on a hosting platform like Heroku or AWS

Find the second largest number in an array of strings.

• Convert the array of strings to an array of numbers.

• Sort the array in descending order.

• Return the second element in the sorted array.

let is block-scoped while var is function-scoped.

• let variables are only accessible within the block they are declared in

• var variables are accessible within the entire function they are declared in

• let variables can be reassigned but not redeclared

• var variables can be both reassigned and redeclared

• let variables are a safer option for avoiding variable hoisting issues

async/await is a syntax for handling asynchronous operations in JavaScript using promises.

• async/await is built on top of promises and provides a more readable and synchronous-like code structure.

• The 'async' keyword is used to define an asynchronous function.

• The 'await' keyword is used to pause the execution of an async function until a promise is resolved or rejected.

• Async functions always return a promise.

• Async/await can be used to handle multiple asynchronous operations in ...read more

Data can be passed from parent component to child component in React using props.

• Parent component can pass data to child component by including it as a prop in the child component's JSX.

• The data can be accessed in the child component using the props object.

• Props are read-only and cannot be modified by the child component.

• Example:

Some common hooks used in React are useState, useEffect, useContext, and useRef.

• useState - used to add state to functional components

• useEffect - used to perform side effects in functional components

• useContext - used to access context in functional components

• useRef - used to create mutable object references in functional components

Flex is one-dimensional layout while Grid is two-dimensional layout.

• Flex is used for creating flexible and responsive layouts.

• Grid is used for creating complex and structured layouts.

• Flex is best suited for small-scale layouts while Grid is best suited for large-scale layouts.

• Flex is easier to learn and implement while Grid requires more advanced knowledge.

• Flex is supported by older browsers while Grid has limited support in older browsers.

Count the number of vowels in a given string

• Iterate through each character in the string and check if it is a vowel (a, e, i, o, u)

• Keep a count of the vowels encountered

• Return the total count of vowels in the string

Constructor in Java is a special type of method that is used to initialize objects.

• Constructor has the same name as the class it belongs to

• It does not have a return type

• It is called when an object of a class is created

• Constructors can be overloaded

SQL stands for Structured Query Language. It is a programming language used for managing and manipulating relational databases.

• SQL is used to communicate with databases and perform various operations like querying, inserting, updating, and deleting data.

• It provides a standardized way to interact with databases, making it easier to work with data.

• SQL is not a programming language in the traditional sense, but rather a language for managing and manipulating data within database...read more

Front end development is the creation of the user interface and user experience of a website or application.

• Involves HTML, CSS, and JavaScript

• Focuses on the visual and interactive aspects of a website or application

• Requires knowledge of design principles and user behavior

• Examples include creating responsive layouts, implementing animations, and optimizing performance

Position sets an element's position relative to its parent, while relative sets an element's position relative to its normal position.

• Position: sets an element's position relative to its parent container

• Relative: sets an element's position relative to its normal position

• Positioned elements are taken out of the normal flow of the document

• Relative elements are still in the normal flow of the document

• Positioned elements can be moved outside of their parent container

• Relative elem...read more

A for loop is used to iterate over a sequence (such as a list, tuple, or string) and perform a set of actions for each item.

• The for loop syntax in Python is: for item in sequence:

• The 'item' variable represents the current item in the sequence.

• The 'sequence' can be any iterable object, like a list or a string.

• Indentation is important in Python, as it defines the block of code to be executed for each iteration.

• The range() function can be used to generate a sequence of numbers t...read more

HTML tags are used to structure content on a web page.

• <h1> - Heading tag

• <p> - Paragraph tag

• <a> - Anchor tag for links

• <img> - Image tag

• <ul> - Unordered list tag

Context provides a way to pass data through the component tree without having to pass props down manually at every level.

• Context is primarily used when data needs to be accessed by many components at different nesting levels.

• It helps in avoiding prop drilling, where props are passed through multiple levels of components.

• Context is created using React.createContext() and accessed using useContext() hook or Consumer component.

Types of variables in JavaScript include var, let, and const.

• var: globally scoped or function scoped

• let: block scoped, can be reassigned

• const: block scoped, cannot be reassigned

JavaScript is a high-level, interpreted programming language that is used to make web pages interactive and dynamic.

• JavaScript is commonly used for client-side web development.

• It can be used to create interactive features like forms, animations, and dynamic content.

• JavaScript can also be used for server-side development with Node.js.

Directives in Angular are markers on a DOM element that tell Angular to attach a specified behavior to that DOM element or transform the DOM element and its children.

• Directives are used to create reusable components or add behavior to existing components.

• There are three types of directives in Angular: Component, Structural, and Attribute directives.

• Examples of directives include ngIf, ngFor, ngStyle, and ngClass.

Anonymous functions are functions that are declared without a name.

• Anonymous functions are often used as arguments to other functions.

• They are commonly used in event handling, callbacks, and closures.

• Example: const add = function(a, b) { return a + b; }

Selectors in CSS are patterns used to select and style HTML elements.

• Selectors are used to target specific elements in an HTML document

• There are different types of selectors like element selectors, class selectors, ID selectors, etc.

• Selectors can be combined to create complex selectors

• Examples: 'h1' selects all h1 elements, '.class' selects elements with a specific class, '#id' selects elements with a specific ID

Navigation serves the purpose of helping users move around a website or application.

• Allows users to easily access different sections of the website

• Helps users understand the structure and hierarchy of the website

• Improves user experience by providing clear and concise directions

• Can include various types of navigation such as menus, breadcrumbs, and search bars

Promises are objects representing the eventual completion (or failure) of an asynchronous operation, while callbacks are functions passed as arguments to be executed after a task is completed.

• Promises provide a more structured way to handle asynchronous operations compared to callbacks.

• Promises can be chained together to handle multiple asynchronous tasks in a more readable manner.

• Callbacks can lead to callback hell, where multiple nested callbacks make the code hard to read ...read more

Lazy loading is a technique used to defer loading of non-essential resources until they are needed.

• Lazy loading can be achieved by using JavaScript to load resources only when they are in the viewport.

• Implementing lazy loading can improve page load times and overall performance.

• Popular libraries like Intersection Observer can be used to implement lazy loading in web applications.

A while loop is a control flow statement that allows code to be executed repeatedly based on a condition.

• The loop continues until the condition becomes false

• The condition is checked before each iteration

• The loop body must include a way to modify the condition to avoid an infinite loop

HTML and CSS are essential languages used for creating and styling web pages.

• HTML (Hypertext Markup Language) is used for structuring content on a web page.

• CSS (Cascading Style Sheets) is used for styling the visual presentation of a web page.

• HTML uses tags to define elements like headings, paragraphs, images, and links.

• CSS controls the layout, colors, fonts, and other visual aspects of a web page.

• Both HTML and CSS are fundamental skills for front end developers.

Middleware in React is a function that intercepts actions before they reach the reducer.

• Middleware allows you to write code that has access to the action that was dispatched and can modify it before it reaches the reducer.

• Commonly used middleware in React includes Redux Thunk and Redux Saga.

• Middleware can be used for logging, crash reporting, asynchronous API calls, and more.

Callback hell is a situation in asynchronous programming where multiple nested callbacks make the code difficult to read and maintain.

• Callback hell occurs when there are multiple levels of nested callbacks in asynchronous code.

• It makes the code difficult to understand, debug, and maintain.

• Promises and async/await are solutions to avoid callback hell.

• Example: nested callbacks in JavaScript AJAX requests.

Create a simple drop down menu using HTML and CSS

• Use element in HTML to create the drop down menuUse elements within the element to define the options in the menu

• Style the drop down menu using CSS to customize its appearance

Debouncing is a technique used to limit the number of times a function is called.

• Debouncing is useful when dealing with events that trigger frequently, such as scrolling or resizing.

• In React, you can implement debouncing using the useEffect hook and a timer.

• Here's an example of debouncing a search input: https://codesandbox.io/s/react-debounce-search-input-4z0jv

Intercepter and class are both used in JavaScript, but serve different purposes.

• Intercepter is used to intercept and modify HTTP requests and responses.

• Class is used to create objects with properties and methods.

• Intercepter is commonly used in frameworks like Angular and React.

• Class is a fundamental concept in object-oriented programming.

• Intercepter can be used to add authentication headers to requests.

• Class can be used to create multiple instances of an object with different...read more

A React counter application that increments and decrements a number.

• Create a state variable to hold the number

• Use the useState hook to update the state

• Render the number and buttons to increment and decrement it

• Add onClick handlers to the buttons to update the state

IT field offers endless opportunities for innovation and growth.

• IT is a constantly evolving field with new technologies and trends emerging regularly.

• IT provides opportunities to work on exciting projects and solve complex problems.

• IT offers a wide range of career paths, from development to design to project management.

• IT is a field that is in high demand, with many job opportunities and competitive salaries.

• IT has the potential to make a significant impact on society and imp...read more

React Redux is a state management library for React applications.

• React Redux is used to manage the state of a React application.

• It provides a predictable state container and allows components to access and update the state.

• Redux follows a unidirectional data flow pattern.

• Actions are dispatched to modify the state, and reducers handle these actions to update the state.

• React Redux provides the 'connect' function to connect components to the Redux store.

• Selectors can be used to ...read more

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

• Promises are used to handle asynchronous operations in JavaScript.

• They can be in one of three states: pending, fulfilled, or rejected.

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

• Example: new Promise((resolve, reject) => { ... }).then(result => { ... }).catch(error => { ... });

let is block scoped, var is function scoped

• let is block scoped, var is function scoped

• let can't be re-declared in the same scope, var can be

• let variables are not hoisted, var variables are hoisted

I am aware of various front end technologies such as HTML, CSS, JavaScript, React, Angular, and Vue.

• HTML

• CSS

• JavaScript

• React

• Angular

• Vue

I have expertise in HTML, CSS, JavaScript, and various front-end frameworks like React and Angular.

• Proficient in HTML, CSS, and JavaScript

• Experience with front-end frameworks like React and Angular

• Knowledge of responsive design and cross-browser compatibility

To implement a timer in React, you can use the useState hook to manage the timer state and useEffect hook to update the timer.

• Use useState hook to initialize timer state

• Use useEffect hook to update timer every second

• Display the timer value in the component's render method