Cryptozookeeper is what I was testing with, and I increased the undo buffer to 4096 so that it would have multiple undos. But I was only testing the beginning of the game, and it’s very conceivable that mid or late game would have different requirements on the undo buffer.
What do you mean by a “js application locally”? The Hugo interpreter could run as a normal web page, just like Quixe, but some extra code would be needed to support that. It won’t be able to run off file: without quite a lot more work because Chrome would block the resource files it requires. As an extension or saved application, yes in theory, but I don’t know what would be needed to set that up.