in Node-Red I find the user function block most usefull.
I'm using it for lots of simple operations like taking a tweet (eg the info from Tue 15 Nov. Vaal Dam Level 14.77m. Full 31.46%. Inflow 165.2m3/s. Discharge 14.39m3/s. River Valves Open 1X100% 1X50%. Gates Open 0. https://twitter.com/VBHydrology/status/798404962229383173)
A similar block in Flow would be most useful