Front-end-Developer-Interview-Questions/questions/javascript-questions.md

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.
• What's the difference between an "attribute" and a "property"?
• Why is extending built-in JavaScript objects not a good idea?
• Difference between document load event and document DOMContentLoaded event?
• What is the difference between == and ===?
• Explain the same-origin policy with regards to JavaScript.
• Make this work:

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?