calling the last callback passed to next multiple times

[timkuijsten]

While implementing native IndexedDB support for Level.js I found that the current implementation might call the last callback that is passed to next() multiple times, instead of exactly once, what I assumed.

I've created a test that checks for this and demonstrates the problem in level.js: timkuijsten/level.js@b27db4b

I've raised this question in Level/level-js#51 (comment) as well.

[vweevers]

This sounds like a problem in the implementation (which calls the callback), not abstract-leveldown. Besides that, level-js has since seen a major upgrade.