When deriving from $page, the derived store will be already avail when $page is still {}/not populated

[205g0]

...which leads to undefined (reading <someProp>) errors. Shouldn't $page call its subs once it's really there / fully populated?

Or can I work-around without using onMount()?

Edit: Adding a $mounted store which is set true within onMount() doesn't work either, I get Cannot access <some derived store from $mounted> before initialization

[205g0]

I think, I've found the condition when this happens: Once you subscribe outside a .svelte file