It may be a little dangerous to rely on these closed over variables to hold your state.

What happens when there are two maps on the same page, and you want double click enabled on only one of them, or you want a different delay on one map?

Someone may naively enable doubleclick for the first map, disable it for the second, and then be incredibly confused when it stops working on the first map.

Unfortunately I don't know enough about Leaflet plugin development, so I don't know the appropriate way to ensure setting apply to only one map.