Every Elm project will define main to be some sort of Program. A Program value captures all the details needed to manage your application, including how to initialize things, how to respond to events, etc.

The type of a Program includes a flags type variable which describes the data we need to start a program. So say our program needs to be given a userID and token to get started:

MyApp.main : Program { userID : String, token : Int }

So when we initialize this program in JavaScript, we can give the necessary flags really easily!

Elm.MyApp.fullscreen({
    userID: "Tom",
    token: 42
});

Head over to the documentation for the Task module for more information on this. It is only defined here because it is a platform primitive.

Head over to the documentation for the Process module for information on this. It is only defined here because it is a platform primitive.

An effect manager has access to a “router” that routes messages between the main app and your individual effect manager.

Send the router a message for the main loop of your app. This message will be handled by the overall update function, just like events from Html.

Send the router a message for your effect manager. This message will be routed to the onSelfMsg function, where you can update the state of your effect manager as necessary.

As an example, the effect manager for web sockets