diff of equal objects should return empty array

[royaldark]

Why does diff({}, {a: 4}) return an array of differences, but diff({}, {}) return undefined? I would expect it to return [] instead.

This makes iteration over the changes much easier. No check for undefined is needed.

We also occasionally use diff only to count the number of differences. This means code like diff(a, b).length will break on equal objects.

[flitbit]

The reason diff({}, {}) returns undefined is because my own prevailing pattern was if(diff(a,b)).

Your diff(a,b).length pattern also makes sense. I'd happily take a PR supporting both patterns. Such could be accomplished by exporting a slightly different accumulateDiff implementation; I'd probably call it listDiff but that's just me.

[webOS101]

I must say I just got bit by this. My build scripts never hit a build that didn't have differences until today and then 💥 . Can you at least update the README to call out this completely unexpected behavior?