It uses continuations to hide the asynchronous nature of web requests and allows the flow between pages of a web app to be written in an imperative style.
There are a couple of continuation-based web frameworks for Ruby (Borges, Wee), but they're old and abandoned as far as I know.
I suspect it didn't catch on because (1) people are afraid of continuations, and (2) web apps are typically designed in at least a pseudo-REST-like style, so the paradigm of "asking" the user (like "await" in ES6) isn't needed very often.
But it's a cool thing to be able to do, especially for funnel-type flows, and other types of more complex session-based interactions.
I wonder if there are any JavaScript inversion of control things for client side code. I've been working for the past week on a signup funnel with React and Flux, and it's just a big explicit state machine... which kind of works, but is also kind of tedious.
There were client side JavaScript continuation like things. Back in the mid-2000's there was Narrative JavaScript. I used it to implement threads and Alice ML style futures/promises on the client side: https://bluishcoder.co.nz/2006/06/05/more-concurrency-in-nar...
