Code Challenge
This code challenge is a bonus round. It does not build on the prior course work and is not necessary to understand future course work. That being said, UTXOs are a common thing in the world of cryptoeconomics and blockchains, so we recommend recommend that you explore them.
UTXOs
Since UTXOs have been around since Bitcoin was first created (2008), there are many great resources on the internet that explain them. There's even Javascript code tutorials and examples that will walk you through how to roll your own. Rather than reinventing the wheel, we're just going to link to a few that we recommend:
Blockchain in JS
A Bitcoin style interactive blockchain demo by nambrot. There's even a tutorial to build your own so you can recreate the demo.
BitcoinJS
A simple UTXO example in Javascript. Their other repos have lots of great examples as well.
How To Code A Bitcoin Blockchain In Javascript
As advertised, a tutorial on how to code a bitcoin blockchain in Javascript. Blockgeeks has more great content, so we recommend you check them out if you want a different perspective on many of the concepts explored in this course.