[kevingadd]

The real problem, design-wise, is that fs.stat operates on a single file at a time. Sometimes you only want info on one file, sure, but in many common use cases, you want info on a bunch of files - perhaps even the contents of an entire directory, or a directory tree. Worse still, stat might be a syscall! Woo, syscall per file.

[jQueryIsAwesome]

... and what does that haves to do with promises?

And in such case you would only do this once outside the listeners of http/or-whatever connections so it would be done just once regardless of the number of concurrent activity.

[kevingadd]

The point is that a properly designed API wouldn't require any amount of scaffolding. You'd go:

    fs.statMany(filenames, function (stats) { ... });

or:

    var statsPromise = fs.statMany(filenames);

And then in either case, you'd just use a for-loop or forEach or whatever your preference on the result. No thinking about how to preserve complex invariants or whatever is necessary.

Hell, with ES6 generator-y expressions you could make it even more succinct, something like:

    var result;
    fs.statMany(filenames, function (stats) { result = [... for x in stats]; });

No push nonsense, no nested if statements, no need to explicitly invoke async.parallel or whatever. Just clarity.

[jQueryIsAwesome]

Sorry, I don't see no clarity there. And how would that fix the fact that stat works in individual files?, and more importantly, how does a function like that handles error? Individual level, group level? It is confusing.