# JS Questions: * Explain event delegation * Explain how `this` works in JavaScript * Explain how prototypal inheritance works * What do you think of AMD vs CommonJS? * Explain why the following doesn't work as an IIFE: `function foo(){ }();`. * What needs to be changed to properly make it an IIFE? * What's the difference between a variable that is: `null`, `undefined` or undeclared? * How would you go about checking for any of these states? * What is a closure, and how/why would you use one? * Can you describe the main difference between a `forEach` loop and a `.map()` loop and why you would pick one versus the other? * What's a typical use case for anonymous functions? * How do you organize your code? (module pattern, classical inheritance?) * What's the difference between host objects and native objects? * Difference between: `function Person(){}`, `var person = Person()`, and `var person = new Person()`? * What's the difference between `.call` and `.apply`? * Explain `Function.prototype.bind`. * What's the difference between feature detection, feature inference, and using the UA string? * Explain Ajax in as much detail as possible. * What are the advantages and disadvantages of using Ajax? * Explain how JSONP works (and how it's not really Ajax). * Have you ever used JavaScript templating? * If so, what libraries have you used? * Explain "hoisting". * Describe event bubbling. * Describe event capturing. * What's the difference between an "attribute" and a "property"? * Why is extending built-in JavaScript objects not a good idea? * Difference between window load event and document DOMContentLoaded event? * What is the difference between `==` and `===`? * Explain the same-origin policy with regards to JavaScript. * Make this work: ```javascript duplicate([1,2,3,4,5]); // [1,2,3,4,5,1,2,3,4,5] ``` * Why is it called a Ternary operator, what does the word "Ternary" indicate? * What is `"use strict";`? what are the advantages and disadvantages to using it? * Create a for loop that iterates up to `100` while outputting **"fizz"** at multiples of `3`, **"buzz"** at multiples of `5` and **"fizzbuzz"** at multiples of `3` and `5` * Why is it, in general, a good idea to leave the global scope of a website as-is and never touch it? * Why would you use something like the `load` event? Does this event have disadvantages? Do you know any alternatives, and why would you use those? * Explain what a single page app is and how to make one SEO-friendly. * What is the extent of your experience with Promises and/or their polyfills? * What are the pros and cons of using Promises instead of callbacks? * What are some of the advantages/disadvantages of writing JavaScript code in a language that compiles to JavaScript? * What tools and techniques do you use debugging JavaScript code? * What language constructions do you use for iterating over object properties and array items? * Explain the difference between mutable and immutable objects. * What is an example of an immutable object in JavaScript? * What are the pros and cons of immutability? * How can you achieve immutability in your own code? * Explain the difference between synchronous and asynchronous functions. * What is event loop? * What is the difference between call stack and task queue? * Explain the differences on the usage of `foo` between `function foo() {}` and `var foo = function() {}` * What are the differences between variables created using `let`, `var` or `const`? * What are the differences between ES6 class and ES5 function constructors? * Can you offer a use case for the new arrow `=>` function syntax? How does this new syntax differ from other functions? * What advantage is there for using the arrow syntax for a method in a constructor? * What is the definition of a higher-order function? * Can you give an example for destructuring an object or an array? * ES6 Template Literals offer a lot of flexibility in generating strings, can you give an example? * Can you give an example of a curry function and why this syntax offers an advantage? * What are the benefits of using `spread syntax` and how is it different from `rest syntax`? * How can you share code between files? * Why you might want to create static class members?