Custom triggers

Hello folks!

We're building a fully serverless Event Store solution here and as part of it, we have to deal with Projections.

Projections happens when an event is written to the Event Store so other parties can do something else (i.e. calculate a materialised view of the event stream).

So, I'm looking to create a trigger that will start a function whenever a projection has to be processed.

I've found this sample https://medium.com/@yuka1984/how-to-make-custom-trigger-with-azure-functions-3bd85551ac5e but it looks like there is no official docs on it.

Can someone point to the right directions on it?

Thanks! Really appreciate any inputs.