Questions About JavaScript

Question 1

Explain event delegation.

Question 2

Explain how prototypal inheritance works.

Question 3

What’s the difference between a variable that is: null, undefined or undeclared? How would you go about checking for any of these states?

Question 4

What is a closure, and how/why would you use one?

Question 5

What language constructions do you use for iterating over object properties and array items?

Question 6

Can you describe the main difference between the Array.forEach() loop and Array.map() methods and why you would pick one versus the other?

Question 7

What’s a typical use case for anonymous functions?

Question 8

What’s the difference between host objects and native objects?

Question 9

Explain the difference between: function Person(){}, var person = Person(), and var person = new Person()?

Question 10

Explain the differences on the usage of foo between function foo() {} and var foo = function() {}

Question 11

Can you explain what Function.call and Function.apply do? What’s the notable difference between the two?

Question 12

Explain Function.prototype.bind.

Question 13

What’s the difference between feature detection, feature inference, and using the UA string?

Question 14

Explain “hoisting”.

Question 15

Describe event bubbling.

Question 16

Describe event capturing.

Question 17

What’s the difference between an “attribute” and a “property”?

Question 18

What are the pros and cons of extending built-in JavaScript objects?

Question 19

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

Question 20

Explain the same-origin policy with regards to JavaScript.

Question 21

Why is it called a Ternary operator, what does the word “Ternary” indicate?

Question 22

What is strict mode? What are some of the advantages/disadvantages of using it?

Question 23

What are some of the advantages/disadvantages of writing JavaScript code in a language that compiles to JavaScript?

Question 24

What tools and techniques do you use debugging JavaScript code?

Question 25

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?

Question 26

Explain the difference between synchronous and asynchronous functions.

Question 27

What is an event loop?

Question 28

What is the difference between call stack and task queue?

Question 29

What are the differences between variables created using let, var or const?

Question 30

What are the differences between ES6 class and ES5 function constructors?

Question 31

Can you offer a use case for the new arrow => function syntax? How does this new syntax differ from other functions?

Question 32

What advantage is there for using the arrow syntax for a method in a constructor?

Question 33

What is the definition of a higher-order function?

Question 34

Can you give an example for destructuring an object or an array?

Question 35

Can you give an example of generating a string with ES6 Template Literals?

Question 36

Can you give an example of a curry function and why this syntax offers an advantage?

Question 37

What are the benefits of using spread syntax and how is it different from rest syntax?

Question 38

How can you share code between files?

Question 39

Why might you want to create static class members?

Question 40

What is the difference between while and do-while loops in JavaScript?