AppBridge is a part of app-sdk npm package. You can import it from "@saleor/app-sdk/app-bridge".
The goal of the AppBridge module is to provide communication (a bridge) between Saleor Dashboard and App.
The whole communication is performed in the browser - it won't work in the Node context.
Docs
The most recent docs can be found in the app-sdk repository.
Events and Actions
AppBridge provides bi-directional communication between Saleor Dashboard and the App (in an iframe context)
Events​
Events are sent from Dashboard, and App can listen to them.
With events, the App can react, e.g., to theme changes or receive a token with a handshake event.
You can find all events here.
Actions​
Actions are sent from App to Dashboard. With actions dispatch, App can ask Dashboard to redirect or show a notification.
You can find all actions here.