I'm really enjoying these minimalist literate programming exercises, so here is another: a minimalist dataflow engine named "dfntly". It is very loosely inspired by the excellent Knockout library, but obviously has much fewer features. I would like to add some support for observable arrays, for example, and for asynchronous calculations where the dataflow engine only calculates further when the reply comes in. But that's something for another day.
In the meantime, if you feel like it, give it a go!