Or .map() as a for..of replacement. I always wanted V8/SpiderMonkey developers to make .map()/.reduce() "pure" in the sense of "optimizing away" the expression if its result is not assigned to anything, and see the world burn.

I'm probably on the mild side of abusing it, I've never seen another developer on my team use it, but I also include self-describing variables for the values. If the reducer function itself is non-trivial, I've give it a name so the final product may look like:

    const idNameMap = itemList.reduce(toIdNameMap)

It should be intuitive that itemList is a list of objects familiar to the context of the code, and the result will be like:

    [{"id1":"Billy"}, etc.