The idea behind redux-saga, to push all effects to the edge (handled by a runtime), only handling descriptions of the actual effects doesn't have to be limited to redux/redux-saga either. You can leverage generators + a runtime to build all kinds of applications like this [0] (you can sort of do this without generators too, but it's a bit more quirky when you cannot control/pause the execution [1]). Easy testing (no more mocks/stubs in the traditional sense - only data/descriptions) and predictability are just some of the benefits.

[0]: https://gist.github.com/eiriklv/a498112b3a73fc2b92975649924c...

[1]: https://gist.github.com/eiriklv/b6cc681447a0939365e1ba044fac...