Some good answers already, but it's worth mentioning that "effects" are managed by Elm's external machinery (the Elm runtime) and delivered to your app via mess

Some good answers already, but it's worth mentioning that "effects" are managed by Elm's external machinery (the Elm runtime) and delivered to your app via messages. There's a really well defined event loop and building apps is accomplished in a very boilerplate (read: consistent) manner. When an update occurs, your app responds to a given message which includes the current app state, and it returns a new state. That state is handed back to the runtime (possibly mutated), and whatever modifications you made will come back around in the next update. http://toreto.re/tea/ http://toreto.re/tea/