chaining `fs.readdir` with a `.then` to return an array

I am trying to create an array of specific files in a directory; which will go through a few test cases to make sure it fits a given criteria.

I'm using the fs.readdir method, but it doesn't return a promise meaning I cannot push to an array.

My idea was to populate an array (arr) with the files I actually want to output and then do something with that array. But because readdir is asynchronous and I can't chain a .then() onto it, my plans are quashed.

I've also tried the same thing with readdirSync to no avail.

via OmisNomis