As already pointed out, these are not the same. Javascript based custom functions in Google Sheets are actually really error prone, meaning that they will just

As already pointed out, these are not the same. Javascript based custom functions in Google Sheets are actually really error prone, meaning that they will just _randomly fail to execute_. Cells will be stuck with a "loading..." message until you trick Sheets into recalculating the value. In the next couple months, I'll likely be ripping out as many custom functions as I can. And these are not for particularly complicated functions. I'd really love to have this feature in Sheets. It would simplify a lot of what my sheets do, and also make it more accessible to a Sheets power user that gets scared off from code.