Enhance PWA Reliability: Start & Fetch Failure Handling

Introduction: The Need for Improved PWA Resilience

In the realm of Progressive Web Apps (PWAs), ensuring a seamless user experience is paramount. One critical aspect of this experience is how the app behaves when faced with connectivity challenges or data integrity issues. Currently, when a user clears their site data and then attempts to launch a PWA while offline, the app often becomes unusable. The service worker, which is crucial for offline functionality, is gone, and the start_url specified in the Web App Manifest cannot be accessed. This results in a generic error page, a situation that can be frustrating for users and undermine their perception of the PWA's reliability. To address this, we propose the implementation of start_failure_callback and fetch_failure_callback properties in the Web App Manifest. These properties will empower developers to gracefully handle startup or fetch failures, providing a much-improved user experience. This enhancement is vital for maintaining user trust and ensuring PWAs deliver on their promise of reliability and functionality, even in challenging network conditions. It allows a PWA to offer a branded recovery experience. This contrasts with the current behavior where the user is presented with a non-descript error page.

The Current Problem with PWA Startup and Data Loss

The current state of PWA behavior in the face of data loss or offline scenarios presents significant challenges. When a user clears all site data, the service worker and cached resources are deleted, and the app loses its offline capabilities. Moreover, when a user tries to launch the PWA while offline, the browser cannot retrieve the start_url from the manifest. This leads to a generic error message, which does not provide any information. This lack of a meaningful recovery mechanism leaves users in the dark. As a consequence, it creates a negative user experience and diminishes the perceived reliability of PWAs. The introduction of start_failure_callback and fetch_failure_callback directly addresses this issue by providing developers with the tools to manage these failure scenarios. The goal is to ensure a better user experience by creating a more resilient PWA and improving its usability. This proactive approach will help PWAs maintain their status as trustworthy and reliable applications.

Detailed Breakdown: The Disrupted PWA User Journey

Consider the typical user journey. A user installs a PWA and adds it to their home screen. Later, they clear their browsing data, which includes all site data. The next time they tap the PWA icon, a series of events happen: the service worker and cache storage are gone, the browser cannot reach the start_url because the user is offline, and a generic error page is displayed instead of the app's usual interface. The consequence is that the PWA appears broken. It leaves the user without an explanation or any opportunity for recovery. The proposed solution is to introduce the start_failure_callback and fetch_failure_callback properties, which specify developer-defined fallback handlers that are executed before any service worker or document fetch occurs. These callbacks allow developers to present a customized message, such as