Nothing trivial about that implementation in my mind - need to keep track of where middleware is registered, reduceRight is non obvious.

I expect these things to be standardized by the framework and all the sharp edges filed off - thats why I go to a framework in the first place.

The reduceRight is just a bit of cute FP code golf. All it’s saying is that chaining an empty list of middleware yields an ‘OK’ response, and that the first middleware is passed a function which, when called, executes the remaining middleware chain, and so on. It would be obvious enough if written out as a for loop, or via direct recursion.

(My username has never been more appropriate!)