beforeinstallprompt doesnt get fired in +layout.svelte

Discussed in https://github.com/sveltejs/kit/discussions/11550

^{Originally posted by rheanV January 9, 2024}
I have an installable PWA (for sveltekit app). I want to add a custom button for installing the app. I placed my window.addEventListener('beforeinstallprompt', (event) => { event.preventDefault(); //logic }); in the onMount of the +layout.svelte file. I have all other configurations correct, meets all installation criteria, and can be installed via the browser download option in the URL bar. However, my "beforeinstallprompt" does not get fired in the +layout.svelte. If I place it in app.html then it is fired but not in +layout.svelte. How should I fix this? What am I missing in my sveltekit app setup?

Start by reviewing the linked discussion and comparing the beforeinstallprompt listener in +layout.svelte's onMount with the working listener in app.html. Trace when each listener is registered relative to the event, then verify the expected behavior in a minimal installable PWA. Done means the issue explains or fixes why the event does not fire from +layout.svelte.