Top 250 JavaScript Interview Questions and Answers

async loads script while page continues to load, defer loads script after page has loaded

• async loads scripts asynchronously while page continues to load

• defer loads scripts after the page has loaded

• async scripts may not execute in order, while defer s...read more

JavaScript can run on servers using server-side JavaScript platforms like Node.js.

• JavaScript can be executed on servers using server-side JavaScript platforms like Node.js.

• Node.js allows JavaScript to run on the server-side by providing a runtime env...read more

JSX is a syntax extension for JavaScript that allows you to write HTML-like code in your JavaScript files.

• JSX stands for JavaScript XML

• It is commonly used with React to define the structure and appearance of components

• JSX elements are transpiled into...read more

setTimeout() is a function in JavaScript that allows you to delay the execution of a function for a specified amount of time.

• setTimeout() takes two parameters: a function to be executed and a delay time in milliseconds

• The function passed to setTimeou...read more

Email validation in JavaScript involves checking if the input follows the correct email format.

• Use a regular expression to check if the email follows the correct format

• Check for the presence of '@' symbol and at least one '.' after it

• Validate the ema...read more

Create a Login form with email validation using Vanilla JS.

• Create a form in HTML with input fields for email and password

• Use JavaScript to validate the email input using regular expressions

• Display error messages if the email input is not in the corre...read more

The .bind() function in jQuery is used to attach an event handler function to one or more elements.

• It allows you to specify the event type and the function to be executed when the event occurs.

• The .bind() function can be used to bind multiple events ...read more

Currying is a technique of transforming a function that takes multiple arguments into a sequence of functions that each take a single argument.

• Currying is achieved by returning a function that takes the next argument until all arguments are received....read more

There is no limit to the number of document ready functions that can be used in a js file.

• Multiple document ready functions can be used to ensure that all necessary elements are loaded before executing code.

• Each document ready function should be encl...read more

Elements in JavaScript can be created using the document.createElement() method.

• Use document.createElement() method to create a new element

• Specify the type of element to be created (e.g. 'div', 'p', 'span')

• Append the newly created element to an exist...read more

clearInterval is a method used to stop the execution of setInterval() method.

• clearInterval() method is used to stop the execution of setInterval() method.

• It takes the ID returned by setInterval() method as a parameter.

• The ID is used to identify the s...read more

Asynchronous tasks in JavaScript allow for non-blocking operations, improving performance and user experience.

• Use callbacks, promises, or async/await to handle asynchronous tasks

• Callbacks: Functions passed as arguments to be executed once the task is...read more

Use window.location.search or URLSearchParams to get URL params in JavaScript

• Use window.location.search to get the query string portion of the URL

• Use URLSearchParams to parse and extract individual parameters from the query string

• Example: const param...read more

Reducer method in JavaScript is used to manage state changes in applications by taking the current state and an action as input and returning a new state.

• Reducer function takes two parameters - the current state and an action

• It then determines how th...read more

Javascript can be used in Selenium to execute scripts and interact with web elements. setValue() method can be used to write values without sendKeys().

• JavascriptExecutor interface can be used to execute Javascript in Selenium

• setValue() method can be ...read more

Nodejs is a runtime environment for executing JavaScript code outside of a web browser.

• Nodejs is built on top of the V8 JavaScript engine

• JavaScript is a programming language used for both front-end and back-end development

• Nodejs allows for server-sid...read more

JS is a scripting language used for web development. Angular is a JS framework for building web applications.

• JS is used for adding interactivity to web pages

• JS has data types like string, number, boolean, etc.

• Angular is a framework for building singl...read more

ES6 introduced many new features like arrow functions, let and const, classes, and more. My favorite feature is template literals.

• Template literals allow for easier string interpolation and multiline strings.

• They use backticks (`) instead of quotes a...read more

JavaScript array methods are built-in functions that allow you to manipulate arrays easily.

• Some common array methods include: push(), pop(), shift(), unshift(), splice(), slice(), concat(), join(), indexOf(), includes(), filter(), map(), reduce().

• Exa...read more

Merge sort is a divide and conquer algorithm that divides the input array into two halves, sorts them, and then merges the sorted halves.

• Divide the array into two halves recursively

• Sort each half using merge sort recursively

• Merge the sorted halves ba...read more

JavaScript methods are built-in functions that can be called on objects to perform specific tasks.

• Methods are called using dot notation, like object.method().

• Some common methods include toString(), toUpperCase(), and includes().

• Methods can also be us...read more

Generators in JavaScript are functions that can be paused and resumed, allowing for asynchronous programming.

• Generators are defined using function* syntax.

• They use the yield keyword to pause execution and return a value.

• Generators can be iterated ove...read more

Inheritance in JavaScript allows objects to inherit properties and methods from other objects.

• Inheritance is achieved through the use of prototypes

• Child objects can access properties and methods of parent objects

• Object.create() and class syntax can b...read more

Form implementation in JS involves creating HTML forms and using JS to handle form submission and validation.

• Create an HTML form with appropriate input fields and submit button

• Use JS to handle form submission and prevent default behavior

• Validate form...read more

Data transfer in ReactJs involves passing data between components using props and state.

• Props are used to pass data from parent to child components

• State is used to manage data within a component and can be passed down as props

• Data can also be transfe...read more

Concurrency in JavaScript refers to the ability of JavaScript to execute multiple tasks simultaneously.

• JavaScript is single-threaded, meaning it can only execute one task at a time.

• Concurrency can be achieved in JavaScript using techniques like Web W...read more

Interfaces in JavaScript allow for defining a contract for objects to implement.

• Interfaces are not natively supported in JavaScript, but can be emulated using object literals and duck typing.

• Interfaces define a set of methods and properties that an o...read more