TIL... Promise.all() returns a Promise

2018-12-17 This post is over 2 years old

This iteration, while writing a series of API calls, I ran into a somewhat silly mistake. I was forking an array of Ids to a set of Promises calling an API using those ids.

I wanted to wait until each call had completed. Then I'd collect the results and returning the aggregate. But what I found was that none of the Promises were resolving in the test.

That's when I discovered I'd made a mistake in my usage of Promise.all(). Promise.all actually returns_another_ promise which resolves when all the given promises resolve. It is not a blocking call. facepalm

So I refactoring the forking function into an async function and awaited on the Promise.all() line. Lo and behold, all the forked promises resolved. I hope this note helps you dodge or resolve a similar goof in the future!