GiGs said: It does, at least in the API (sheet workers have a few gaps). I don't know the exact version of JavaScript supported, but I had a quick look at feature sets, and it includes at least some features of ES9. Are these ES9 features also present in sheetworkers? And what known gaps does the sheetworkers have? I updated the Sheet Worker Scripts page to mention that they have access to the underscore library, but it would be great if we could update the documentation to mention what we have access to in sheetworker and the API.