Using `TransformStream`s to build a pub/sub library (gist.github.com)

`TransformStream`s in JavaScript provide a built-in mechanism for transforming data. Since a TransformStream` contains both a writable and a readable side, where anything written to the writable side is emitted from the readable side, it effectively acts as an `Obserbavle`. This makes it well-suited for implementing a simple pub/sub system, where data can be published via the writable end and subscribed to via the readable end.