A Quick Review (v1)


This course assumes that you have a decent grasp on the fundamentals of JavaScript. If you have recently taken our JavaScript fundamentals series then you will be in good shape to continue here. If it’s been a while, you will probably want to take a day or two to study a few concepts and refresh yourself on the basics.


Read the Occurrences of undefined in the language section of this article by Dr. Axel Rauschmayer and make sure you understand the cases where the language returns the undefined value.

To make sure that you understand and remember the cases mentioned in the article create at least two examples for each occurrence and keep these examples in your notes. (You keep notes, don’t you?)

It’s also worth bookmarking this article and reading it after you have completed the JavaScript course, as it contains some advanced topics that we haven’t touched yet.


Running through "part 1" of MDN’s JavaScript basics course or doing the Basic JavaScript portion of FreeCodeCamp is a great idea for a refresher on the syntax. If you just want a quick reference to skim, try LearnXinY.

It might also be a good idea to do a little practicing before moving on. It may be a good idea to redo one of the later projects from our fundamentals course such as the calculator or rock-paper-scissors. If you want something fresh to work on, now would be a fine time to do some coding exercises from across the net. The following sites are all great places to look.

  • Exercism
  • CodeWars
  • FreeCodeCamp (especially their "Object Oriented", "Functional Programming", and "Algorithm Scripting" sections)
  • JavaScript30 is a great set of tutorials that cover a ton of JS concepts.

UPDATED: 02.02.2021