Built-in Coeffects in re-om

:db

The :db coeffect is used to retrieve the whole app-state.

The data associated to a :db coeffect is a map that is the current value of the whole app-state.

The :db coeffect is automatically injected by re-om into the coeffects map so you don't need to inject this coeffect when we define an event handler,

The event handler for the ::set-screen-size event below is getting the current app-state inside the coeffects map (the first parameter of any event handler) thanks to the :db coeffect and then resetting the app-state using the :db effect.

(re-om/register-event-handler!
 ::set-screen-size
 (fn [{:keys [db]} [size]]
   {:db (assoc db ::screen-size size)}))