Understanding Immutable.js's Map() and List() structures will likely take you as far as you want to go with immutable programming. They have only small semantic differences between each other and the remaining structures in the Immutable.js family. Sequence, however, has one major difference: it's lazy--which opens a new realm of functional possibilities. Let's write a simple sequence to start.
I think the real problem is that people running this web service don't check the quality of contents each instructor created and publish online. It's okay for instructors to make mistakes as long as they are fixed before the contents are published. I regret that I've paid the fee to use this service annually.