Why not a strict comparison to undefined here?

I reserve those for cases where we explicitly want to differentiate null and undefined in order to keep the minified output more compressible. Each === undefined costs about a byte.

I'm okay with that as long as we document it somewhere. The first thing I did when I saw this was look for a place where it might be assigned null thinking the check for both was important. The style guide example implies we do it to check for both.

Any thoughts on how to document it? I see what you mean about the style guide, and even though this technically fits because I'd allow null to pass, the fact is that it will never come up so it's arguably against the spirit of our style guide. I could also just suck it up and use === undefined if you think the current approach is confusing.

What does everyone else think? To me the === undefined is clearer and worth a byte.

I'm ambivalent. I'd be fine with whichever.