As a followup to the Native-Decker incarnation of the "danger" interface, I've created a counterpart for Web-Decker which allows Lil and JS to interoperate, opening the door for bodging in access to all sorts of web APIs that are normally not accessible via Lil.
danger.js["f=>f(f(47))" (on twice x do x,x end)] # (47,47,47,47)
Just like the native "danger" interface, this feature is strictly opt-in and available to those who build Decker from source. Using this will severely limit portability of your decks, and offer many footguns for breaking the Decker environment. It is, however, significantly lower risk than the native "danger zone", since it's still answerable to the sandboxing mechanisms of a web browser. It was always possible to do this sort of thing by manually editing .html Decker exports, but this mechanism makes it possible to write those sorts of "plugins" against a stable internal interface.
Docs are updated here, for reference.