used for client bootstrap and starts recording events 2. Browser makes async requests for additional assets (i.e. images, JS, CSS, etc.) 3. Once external resources loaded, Angular client bootstrapping begins 4. Client view rendered to the hidden div created by Preboot 5. Bootstrap complete, so Angular client calls preboot.done() 6. Preboot events replayed in order to adjust the application state to reflect changes made by the user before Angular bootstrapped (i.e. typing in textbox, clicking button, etc.) 7. Preboot switches the hidden client view div for the visible server view div https://universal.angular.io/overview/