Skip to content

InterviewPrep.World

Main Navigation React Angular JavaScript TypeScript System Design HR Search

Appearance

♥ Sponsor

Sidebar Navigation

Overview

JavaScript Basics

All JavaScript Basics

What are the JavaScript primitive types?

What is the difference between `==` and `===`?

What is the difference between `null` and `undefined`?

What is hoisting in JavaScript?

What is the temporal dead zone?

How do `var`, `let`, and `const` differ?

What is strict mode?

What is type coercion?

What makes a value truthy or falsy?

What is the difference between shallow and deep equality?

Functions & Scope

All Functions & Scope

What is a closure?

What is lexical scope?

What is the difference between `call`, `apply`, and `bind`?

What is a higher-order function?

What is currying?

What is function composition?

How do arrow functions handle `this`?

What is an IIFE?

What is a pure function?

What is the difference between a callback and a promise?

Async JavaScript

All Async JavaScript

What is the JavaScript event loop?

What is the difference between the microtask and macrotask queues?

What are the states of a Promise?

How does `async`/`await` work?

What is the difference between `Promise.all` and `Promise.allSettled`?

When would you use `Promise.race` or `Promise.any`?

How do you handle errors with async/await?

What is callback hell and how do you avoid it?

How do you cancel a fetch request?

What is the difference between synchronous and asynchronous code?

Prototypes & OOP

All Prototypes & OOP

What is the prototype chain?

What is the difference between `__proto__` and `prototype`?

How does `new` work?

What are JavaScript classes syntactic sugar for?

What is prototypal inheritance?

How do you create an object without a prototype?

What is the difference between own and inherited properties?

How does `instanceof` work?

What are getters and setters?

When should you prefer composition over inheritance?

ES6+ Features

All ES6+ Features

What are ES modules?

What is the difference between default and named exports?

What are template literals?

What are destructuring assignments?

What is the rest parameter?

What is the spread operator?

What are `Map` and `Set` useful for?

What are `WeakMap` and `WeakSet`?

What are generators and iterators?

What are optional chaining and nullish coalescing?

DOM & Browser APIs

All DOM & Browser APIs

What is event delegation?

What is the difference between event bubbling and capturing?

What do `preventDefault` and `stopPropagation` do?

What is the difference between an attribute and a property?

When does `DOMContentLoaded` fire?

How do you create and insert DOM elements safely?

What is the difference between `innerHTML`, `textContent`, and `innerText`?

How do you use `data-*` attributes?

What is the browser rendering pipeline?

What is a Web Worker?

Performance

All Performance

What causes a memory leak in JavaScript?

What is debouncing?

What is throttling?

What is memoization?

What is a layout thrash?

How can you avoid unnecessary reflows and repaints?

What is code splitting?

What is tree shaking?

How do you profile a slow web page?

When should you use `requestAnimationFrame`?

Security

All Security

What is the same-origin policy?

What is CORS?

What is cross-site scripting (XSS)?

How do you prevent XSS in a web application?

What is CSRF and how can it be mitigated?

Why is `eval` dangerous?

How should sensitive data be stored in the browser?

What are secure cookie attributes?

What is Content Security Policy?

How do you validate and sanitize user input?

Design Patterns

All Design Patterns

What is the module pattern?

What is the observer pattern?

What is the pub/sub pattern?

What is the factory pattern?

What is the singleton pattern and its trade-offs?

What is the strategy pattern?

What is the adapter pattern?

What is dependency injection in JavaScript?

What is immutability and why does it matter?

How do you design a reusable API client?

Coding Challenges

All Coding Challenges

How do you flatten a nested array?

How do you implement debounce?

How do you implement deep clone?

How do you group an array of objects by a key?

How do you find duplicate values in an array?

How do you implement `Array.prototype.map`?

How do you implement a Promise pool with concurrency limits?

How do you write a memoize function?

How do you compare two objects deeply?

How do you implement an event emitter?

On this page

JavaScript Basics

Browse questions in this section. Start here.

Last updated:

Pager

Previous pageOverview

Next pageWhat are the JavaScript primitive types?

Built for developers preparing for technical interviews.

JavaScript Basics ​

JavaScript Basics