As I was doing my research for the article, I found a lot of things that really surprised me. And I feel pretty confident in saying that most web developers aren't aware of these things either.
Here are my top four:
- We shouldn't use the unload event. Ever.
- The unload event often doesn't fire when closing tabs/app on mobile
- The pagehide/pageshow events even exist (virtually no one I've talked to knows what they do; most people think they're about page visibility).
- In browsers that implement a page navigation cache, you can click a link to navigate away and then navigate back with the back button, and all your JS code is exactly as it was before you navigated.
To this last point. Try doing this in the console:
1. Write a promise that resolves in a setTimeout after 5 seconds.
2. After 1 second, click a link to navigate to a new page.
3. Stay on that page for an hour.
4. Click that back button.
5. Your promise will resolve in 4 seconds!