The pitfalls of the online and offline browser events

The obvious solution for tracking offline usage is to create event listeners for the online and offline events (which many browsers support) and to put your analytics tracking logic in those listeners. Unfortunately, there are several problems and limitations with this approach:

• In general tracking every network connection status event might be excessive, and is counter-productive in a privacy-centric world where as little data as possible should be collected. Additionally the online and offline events can fire for just a split second of network loss, which a user probably wouldn't even see or notice.
• The analytics tracking of offline activity would never reach the analytics server because the user is… well, offline.
• Tracking a timestamp locally when a user goes offline and sending the offline activity to the analytics server when the user goes back online depends on the user revisiting your site. If the user drops off your site due to a lack of an offline mode and never revisits, you have no way to track that. The ability to track offline drop-offs is critical data for building a case about why your site needs a better offline mode.
• The online event is not very reliable as it only knows about network access, not internet access. Therefore a user might still be offline, and sending the tracking ping can still fail.
• Even if the user still stays on the current page while being offline, none of the other analytics events (e.g. scroll events, clicks, etc.) are tracked either, which might be the more relevant and useful information.
• Being offline in itself is also not too meaningful in general. As a website developer it may be more important to know what kinds of resources failed to load. This is especially relevant in the context of SPAs, where a dropped network connection might not lead to a browser offline error page (which users understand) but more likely to random dynamic parts of the page failing silently.

You can still use this solution to gain a basic understanding of offline usage, but the many drawbacks and limitations need to be considered carefully.