Learn / JavaScript Fundamentals
Values & arrays
The data structures you'll touch in every JavaScript program. A class in JavaScript Fundamentals. Free to start, no card.
Curated lessons in this class
JavaScript: array methods
map, filter, and reduce without a loop in sight.
- console.log
- map
- filter
- reduce
The bug a passing test cannot see
A function returns the right answer and still corrupts your data.
- Prove the damage
- Fix it without changing what it returns
- Write the check that would have caught it
- The same trap, somewhere else
Also coming to this class
How CodeTrain teaches this
No videos and no multiple-choice quiz at the end. Each lesson is a handful of small steps in a real editor. You type the code yourself, it runs, and the tutor reviews what you actually wrote. It will not hand you the answer, and the step doesn't advance until your code passes. What you get at the end is a record of which steps you wrote unaided, not a completion percentage.
These curated courses are the starting point, not the product
Everything in this catalog is a curated course we wrote by hand. They exist so there is something to start on. What CodeTrain actually does is build a lesson on demand: name any topic you want to understand and it writes one for you on the spot, or paste any public repository and it teaches you that codebase from the code that is really in it. You are not limited to the list below, and most people stop using it within a session or two.