Top 250 JavaScript Interview Questions and Answers

IIFE stands for Immediately Invoked Function Expression. It is a JavaScript function that is executed as soon as it is defined.

• IIFE is a way to create a function expression and immediately invoke it.

• It helps in creating a private scope for variables ...read more

Freeze an object in JavaScript and access a nested property value.

• Use Object.freeze() to prevent modifications to the object.

• Access the nested property using dot notation: val.a.b.

• Example: const value = val.a.b; // value will be 5.

• Attempting to chang...read more

Prototype chain in JavaScript is the mechanism by which objects inherit properties and methods from other objects.

• In JavaScript, each object has a private property which holds a link to another object called its prototype.

• If a property or method is n...read more

Calling a function using the new keyword creates a new instance of the function's constructor.

• Creates a new empty object

• Binds 'this' to the new object

• Adds a property to the new object called '__proto__' which points to the constructor function's prot...read more

JS stands for JavaScript, a programming language used for web development. QP stands for Query Parser, a tool used for parsing and analyzing queries.

• JS is a programming language used for web development.

• QP is a tool used for parsing and analyzing que...read more

Microservices in JavaScript are small, independent, and loosely coupled services that work together to form a larger application.

• Microservices are designed to be modular and scalable

• Each microservice performs a specific task and communicates with oth...read more

Error handling in JavaScript involves using try-catch blocks, throwing errors, and using error objects.

• Use try-catch blocks to catch errors and handle them gracefully

• Throw errors using the throw keyword to indicate when something goes wrong

• Use error ...read more

Bind creates a new function with a specified 'this' value and arguments.

• Bind returns a new function with the same body as the original function.

• The 'this' value of the new function is bound to the first argument passed to bind().

• The subsequent argume...read more

Multithreading is not natively supported in JavaScript, but can be achieved through Web Workers.

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

• Web Workers allow for multithreading in JavaScript by running scr...read more

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

• NodeJS allows JavaScript to be run on the server-side, enabling backend development.

• NodeJS has a built-in library of modules that can be easily integrated into app...read more

Sets in JavaScript are used to store unique values of any type.

• Create a new set using the Set constructor

• Add values to the set using the add() method

• Check if a value exists in the set using the has() method

• Remove a value from the set using the delete...read more

Exceptions in JavaScript can be handled using try-catch blocks.

• Use try-catch blocks to catch and handle exceptions in JavaScript.

• The try block contains the code that may throw an exception.

• The catch block is used to handle the exception if one occurs...read more

Modules in JavaScript are reusable pieces of code that can be exported from one file and imported into another.

• Modules help in organizing code into separate files for better maintainability.

• Modules can be imported using 'import' keyword and exported ...read more

Recreating tic tac toe game in plain JavaScript

• Create a 3x3 grid using HTML and CSS

• Use JavaScript to handle player turns and check for win conditions

• Implement a reset button to start a new game

Data types in JavaScript include number, string, boolean, object, function, undefined, and null.

• Number - represents numeric data, e.g. 10, 3.14

• String - represents textual data, e.g. 'hello', '123'

• Boolean - represents true or false values, e.g. true, ...read more

Polyfills are code that provide modern functionality on older browsers that do not natively support it.

• Polyfills are used to fill in the gaps for browser compatibility by replicating the functionality that is missing in older browsers.

• They are typica...read more

The method used to submit forms in JavaScript is the submit() method.

• The submit() method is called on the form element.

• It can be triggered by a button click or programmatically.

• Example: document.getElementById('myForm').submit();

The __proto__ is a property that points to the prototype of an object, while prototype is a property of a constructor function.

• The __proto__ property is used to access the prototype of an object.

• The prototype property is used to add properties and me...read more

Creating a prototype in JavaScript

• Use the Object.create() method to create a prototype object

• Add properties and methods to the prototype object

• Use the prototype object to create new instances of an object

package.json is a configuration file used in Node.js projects to manage dependencies and scripts.

• Contains metadata about the project such as name, version, and author

• Lists dependencies and devDependencies required for the project

• Allows for the creati...read more

Use the delay() method in jQuery to add delay for animation.

• Use the delay() method before the animation function.

• Specify the duration of the delay in milliseconds as an argument.

• Example: $(element).delay(1000).fadeOut();

Arrow functions are a concise way to write functions in JavaScript.

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

• They do not have their own 'this' keyword, instead they inherit 'this' from the parent scope.

• Arrow f...read more

JavaScript DOM stands for Document Object Model, which represents the structure of a web page as a tree of objects.

• DOM is a programming interface for web documents.

• It allows scripts to dynamically access and update the content, structure, and style o...read more

Throttling in JavaScript is a technique used to control the rate at which a function is executed.

• Throttling limits the number of times a function can be called over a specified period.

• It is commonly used in scenarios like scroll events, resize events...read more

The onbeforeunload method is used to prevent form save.

• Use the onbeforeunload method to display a warning message before leaving the page without saving the form.

• Return a custom message in the method to prompt the user to confirm if they want to leav...read more

Optional chaining is a feature in JavaScript that allows you to access properties of an object without worrying about whether the object is null or undefined.

• It uses the question mark (?) operator to check if a property exists before accessing it.

• It ...read more

ES6 introduces new syntax and features to JavaScript.

• Arrow functions

• Template literals

• Let and const keywords

• Destructuring assignment

• Default parameters

• Rest and spread operators

• Classes

• Modules