Suggestion: External sheets.

[everythingability]

I don't know if this is possible, or advisable...

I just went to create a web app - but not in the sheet that I wanted to connect to... would it be possible to do this...

const ss = SpreadsheetApp.openById("MY_ID")
const gq = new GQuery(ss);

.... with the behaviour being, if nothing is supplied use the active spreadsheet, if not use the one supplied. Maybe the ID could be passed also perhaps?

[imreallyliam]

Actually, I hadn't documented this, but you almost had the exact formatting of the behavior. You can just use:
new GQuery("MY_ID")

I don't use it too often, but sometimes I have needed it. It'll automatically switch and do the work of using spreadsheetapp to open the sheet, or throw an error if the sheet doesn't exist. Let me know if it works, if so, I will add it to the README as well so others are aware.

[everythingability]

Ah! Fabulous.... thanks, will do.