A system for composing browser-based applications is enhanced with cross-tab communication capability. At design time, responsive to a configuration instruction from a user, the system configures a user interface (UI) event for a browser-based application such that the UI event is publishable across all open browser tabs at application runtime. Responsive to a publication instruction from the user, the system configures a first application page to generate the UI event at application runtime in response to a trigger and to publish the UI event to browser local storage. Responsive to a subscription instruction from the user, the system configures a second application page to periodically poll the browser local storage for the user interface event at application runtime and, in response to the UI event published by the first application page to the browser local storage, process the UI event and automatically immediately update the second application page.