30-seconds-of-interviews

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A curated collection of common interview questions to help you prepare for your next interview.

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143 links in 110 sections, with live GitHub stats.activeno commit in 2y

React docs on State and Lifecycle

MDN docs for comparison operators

React docs on State and Lifecycle

Official Web Docs Promise

MDN docs for typeof

Cross-Site Scripting Attack (XSS)

MDN docs for CORS

MDN docs for DOM

let vs const

Event Delegation

React docs on setState

What is the difference between a statement and an expression?

Similar problem
122.1Kalmost 2 years

A simple helper function to check equality
122.1Kalmost 2 years
Fix "0.1 + 0.2 = 0.300000004" in JavaScript

JavaScript: What is short-circuit evaluation?

MDN docs for hoisting

React docs on Handling Events

MDN docs for closures

Automatic semicolon insertion in JavaScript

React docs on Conditional Rendering

React docs on Lists and Keys

Mozilla Docs Closures & Lexical Scoping

JavaScript Value vs Reference

MDN docs for inheritance and the prototype chain

MIME Type MDN

Master the JavaScript Interview: What is a Promise?

MDN docs for callbacks

JavaScript Value vs Reference

React docs on Handling Events

React docs on Fragments

What is function composition?

Node.js docs on event loop, timers and process.nextTick()

MDN docs for NaN

Mutating vs non-mutating array methods

Big O Notation in JavaScript

Pure functions in JavaScript

In plain English, what is recursion?

Implementing memoization in JavaScript

React docs on Refs and the DOM

Declarative vs Imperative Programming

React docs on Portals

React docs on Context

Classes on MDN

this on MDN

React docs on Children

React docs on Refs and the DOM

Virtual DOM in Hyperapp
19.1Kalmost 2 years

MDN docs for strict mode

The difference between Virtual DOM and DOM

React docs on State and Lifecycle

React docs on State and Lifecycle

React docs on Handling Events

React docs on setState

React docs on Handling Events

React docs on Conditional Rendering

React docs on Lists and Keys

React docs on Refs and the DOM

React docs on Fragments

https://reactjs.org/docs/error-boundaries.html

React docs on Context

React docs on Refs and the DOM

React docs on Children

React docs on Portals

A good basis for accessibility

Strategies for cache-busting CSS

StackOverflow Using header or footer tag twice

HTML 5 Semantic Elements

async vs defer attributes

React docs on Handling Events

W3Schools docs for HTML and XHTML

MDN docs for DOM

HTML 5.2 WWW Specifications

W3Schools HTML5 Webstorage

Writing clean and maintainable CSS

CSS Preprocessors

CSS units for font-size: px | em | rem

CSS Sprites explained by CSS Tricks

CSS Specificity

:focus-visible

Accessibility APIs

https://medium.com/extend/what-is-rest-a-simple-explanation-for-beginners-part-1-introduction-b4a072f8740f
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Node.js docs on event loop, timers and process.nextTick()

Cross-Site Scripting Attack (XSS)

Featured in 2 awesome lists

Each link jumps to the spot where the list mentions 30-seconds-of-interviews.

What's in the list

Contributing

JavaScript / What is a stateless component?

JavaScript / What is the difference between the equality operators == and ===?

JavaScript / What is the difference between an element and a component in React?

JavaScript / What is a stateful component in React?

JavaScript / In which states can a Promise be?

JavaScript / What does the following code evaluate to?

JavaScript / How do you clone an object in JavaScript?

JavaScript / How do you compare two objects in JavaScript?

JavaScript / What is a cross-site scripting attack (XSS) and how do you prevent it?

JavaScript / What is CORS?

JavaScript / What is the DOM?

JavaScript / What are the differences between var, let, const and no keyword statements?

JavaScript / What is event delegation and why is it useful? Can you show an example of how to use it?

JavaScript / What is the purpose of callback function as an argument of setState?

JavaScript / What is the difference between an expression and a statement in JavaScript?

JavaScript / What are truthy and falsy values in JavaScript?

JavaScript / Generate an array, containing the Fibonacci sequence, up until the nth term.

JavaScript / What does 0.1 + 0.2 === 0.3 evaluate to?

JavaScript / What is the difference between the array methods map() and forEach()?

JavaScript / What is short-circuit evaluation in JavaScript?

JavaScript / What will the console log in this example?

JavaScript / How does hoisting work in JavaScript?

JavaScript / What is the difference between HTML and React event handling?

JavaScript / What is the reason for wrapping the entire contents of a JavaScript source file in a function that is immediately invoked?

JavaScript / What does the following function return?

JavaScript / What are inline conditional expressions?

JavaScript / What is a key? What are the benefits of using it in lists?

JavaScript / What is the difference between lexical scoping and dynamic scoping?

JavaScript / What is the output of the following code?

JavaScript / How does prototypal inheritance differ from classical inheritance?

JavaScript / What is a MIME type and what is it used for?

JavaScript / What are Promises?

JavaScript / What are JavaScript data types?

JavaScript / NodeJS often uses a callback pattern where if an error is encountered during execution, this error is passed as the first argument to the callback. What are the advantages of this pattern?

JavaScript / What is a callback? Can you show an example using one?

JavaScript / What is the difference between null and undefined?

JavaScript / Does JavaScript pass by value or by reference?

JavaScript / How do you pass an argument to an event handler or callback?

JavaScript / What are fragments?

JavaScript / Create a function pipe that performs left-to-right function composition by returning a function that accepts one argument.

JavaScript / What is the event loop in Node.js?

JavaScript / What is the only value not equal to itself in JavaScript?

JavaScript / Contrast mutable and immutable values, and mutating vs non-mutating methods.

JavaScript / What is Big O Notation?

JavaScript / What is a pure function?

JavaScript / What is recursion and when is it useful?

JavaScript / What is memoization?

JavaScript / What are refs in React? When should they be used?

JavaScript / Explain the differences between imperative and declarative programming.

JavaScript / What is functional programming?

JavaScript / What are portals in React?

JavaScript / What is event-driven programming?

JavaScript / What is context?

JavaScript / Explain the difference between a static method and an instance method.

JavaScript / What is a closure? Can you give a useful example of one?

JavaScript / What is the this keyword and how does it work?

JavaScript / What is the children prop?

JavaScript / Which is the preferred option between callback refs and findDOMNode()?

JavaScript / What is the purpose of JavaScript UI libraries/frameworks like React, Vue, Angular, Hyperapp, etc?

JavaScript / What does 'use strict' do and what are some of the key benefits to using it?

JavaScript / How can you avoid callback hells?

JavaScript / What is a virtual DOM and why is it used in libraries/frameworks?

JavaScript / How do you ensure methods have the correct this context in React component classes?

React / What is a stateless component?

React / What is a stateful component in React?

React / What is the difference between an element and a component in React?

React / How do you pass an argument to an event handler or callback?

React / What is the purpose of callback function as an argument of setState?

React / What is the difference between HTML and React event handling?

React / What are inline conditional expressions?

React / What is a key? What are the benefits of using it in lists?

React / Which is the preferred option between callback refs and findDOMNode()?

React / What are fragments?

React / How do you ensure methods have the correct this context in React component classes?

React / What are error boundaries in React?

React / What is context?

React / What are refs in React? When should they be used?

React / What is the children prop?