> I'm really unclear on how the zone library is doing the magical interception of errors It monkey patches the entry points into javascript from the binding l

> I'm really unclear on how the zone library is doing the magical interception of errors It monkey patches the entry points into javascript from the binding layer (some wrapping happens at a higher level), for the purpose of keeping track of the active zone. At that level we also wrap a try-catch block around all callbacks. > Does a library (say, one that came from npm and not the core library) have to be zone-aware to function correctly with zones It depends. Most modules shouldn't need any modification. However there are certain not-so-common cases (for example, when you're implementing a connection pool) that the module would need to be made zone-aware. It's necessary when the module wants to call a callback (or any function) in a child zone from a parent/ancestor zone. Right now that's not very easy - you'd have to use a Gate (https://github.com/strongloop/zone#gates https://github.com/strongloop/zone#gates). W're working on an easier API.