Excellent article! Loved it! As others said, looking forward for more of these articles!

One quick feedback though: there seems to be some issue with the JSBin link in the “Designing Observable: Ergonomic Observer Safety” section. (Namely this one: JSBin example to show the minimal Observable implementation). It does not produce the desired output. The Observable class lacks the subscribe method definition and the correponding call at the end. It’s fixed in the next link (the one about the map operator).