Top 250 JavaScript Interview Questions and Answers

Debouncing in JavaScript is a technique used to limit the number of times a function is called in a short period of time.

• Debouncing is used to improve performance and prevent unnecessary function calls.

• It delays the execution of a function until afte...read more

JavaScript in HTML is a scripting language used to add interactivity and dynamic content to web pages.

• JavaScript is a programming language that can be embedded directly into HTML code

• It allows for interactive elements like pop-up alerts, form validat...read more

Yes, JavaScript code can be broken into several lines for better readability and organization.

• JavaScript code can be broken into multiple lines using line breaks or the backslash character.

• Line breaks are automatically interpreted as the end of a sta...read more

Creating a dummy website involves designing and developing a basic website for testing purposes.

• Choose a simple layout and design for the website

• Include placeholder content and images

• Ensure basic functionality like navigation and links work

• Use dummy ...read more

Local Storage is persistent storage that remains even after the browser is closed, while Session Storage is temporary and is cleared when the browser is closed.

• Local Storage has no expiration date, while Session Storage is cleared when the session en...read more

You can change the background color of all items in JavaScript by selecting all elements and setting their background color property.

• Select all elements using document.querySelectorAll()

• Loop through the selected elements and set their style.backgroun...read more

Select all div using jQuery

• Use the jQuery selector $('div') to select all div elements

• This will return a jQuery object containing all the selected div elements

• You can then perform operations on the selected div elements using jQuery methods

The return type of getElementsByClassName method in JavaScript is an array of elements.

• The method returns an array of elements that have a specified class name.

• The elements are returned in the order they appear in the document.

• If no elements are foun...read more

Ajax can be used to upload files without refreshing the page.

• Create a form with file input and submit button.

• Use FormData object to collect form data.

• Send data to server using Ajax.

• Handle file upload on server side.

• Return response to client and updat...read more

Call, apply, and bind are methods in JavaScript used to manipulate the context of a function.

• Call: Invokes a function with a specified 'this' value and arguments provided individually.

• Apply: Invokes a function with a specified 'this' value and argume...read more

Create a tab section using JavaScript

• Use HTML and CSS to create the tab structure

• Use JavaScript to handle the tab functionality

• Add event listeners to the tab elements to switch between tabs

Web workers are JavaScript scripts that run in the background, separate from the main browser thread.

• Web workers allow for parallel execution of tasks, improving performance and responsiveness.

• They can perform computationally intensive tasks without ...read more

Promises in JavaScript are used to handle asynchronous operations and avoid callback hell.

• Promises represent a value that may not be available yet but will be resolved at some point in the future.

• They have three states: pending, fulfilled, or rejecte...read more

AJAX (Asynchronous JavaScript and XML) is a technique used in web development to create asynchronous web applications.

• AJAX allows web pages to be updated asynchronously by exchanging data with a web server behind the scenes.

• It enables web pages to be...read more

Decorators in JavaScript are functions that allow you to add new functionality to existing objects or functions.

• Function decorators: Functions that take another function as an argument and return a new function that adds some kind of behavior.

• Class d...read more

Spread operator expands elements, while rest operator collects them into an array.

• Spread Operator: Used to expand elements of an iterable (like an array) into individual elements.

• Example: const arr = [1, 2, 3]; console.log(...arr); // Outputs: 1 2 3

• R...read more

Arrow functions are used for concise syntax, lexical scoping of 'this', and implicit return of single expressions.

• Arrow functions have a more concise syntax compared to traditional function expressions.

• Arrow functions do not bind their own 'this' val...read more

Temporal dead zone (TDZ) is a behavior in JavaScript where variables are inaccessible before their declaration.

• TDZ occurs with 'let' and 'const' declarations in JavaScript.

• Example: In 'console.log(x); let x = 5;', this will throw a ReferenceError.

• TDZ...read more

Yes, it is possible to connect to a database using JavaScript.

• JavaScript can connect to databases using APIs such as Web SQL, IndexedDB, and MongoDB.

• It is also possible to use Node.js to connect to databases using JavaScript.

• However, it is not recomm...read more

Performance in React JS can be improved by optimizing rendering, reducing unnecessary re-renders, using virtualization, code splitting, and lazy loading.

• Optimize rendering by using shouldComponentUpdate or React.memo

• Reduce unnecessary re-renders by u...read more

The mostly used design patterns in JavaScript are Module, Observer, Singleton, Factory, and Prototype.

• Module pattern helps to keep the code organized and maintainable.

• Observer pattern is used for event handling and notification.

• Singleton pattern rest...read more

JS hoisting is a mechanism where variable and function declarations are moved to the top of their scope.

• Variable declarations are hoisted but not their values

• Function declarations are fully hoisted

• Let and const declarations are not hoisted

Yes, R can be integrated with JavaScript using the 'shiny' package to create interactive web applications.

• Use the 'shiny' package in R to create interactive web applications

• Use the 'htmlwidgets' package to embed interactive R visualizations in web pa...read more

Polyfills are code that allows modern browsers to support features that are not natively supported.

• Polyfills are used to bridge the gap between modern web development and older browsers.

• They provide a way to use new features without worrying about br...read more

Let, Const, and Var are used to declare variables in JavaScript with different scoping and reassignment abilities.

• Var has function scope and can be redeclared and reassigned.

• Let has block scope and can be reassigned but not redeclared.

• Const has block...read more

Webpack is a module bundler for JavaScript applications.

• Webpack takes modules with dependencies and generates static assets representing those modules.

• It can handle various types of assets like JavaScript, CSS, and images.

• Webpack allows for code spli...read more

The 'this' keyword in JS 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 the method belongs to.

• In a regular function, 'this' refers to the...read more