How was this repro created

First, I installed svelte kit

npm create svelte@latest store-bug

Then, I edited src/routes/+page.svelte to set a context containing a store.

Lastly, I created src/routes/ChildComponent.svelte that gets the context containing the store, and subscribes to it.

Then, run with

yarn dev

and load the page.

What is the bug?

Per the documentation about the derived store, the callback should be evaluated lazily:

The callback runs initially when the first subscriber subscribes and then whenever the store dependencies change.

However, in this repro I am seeing that on the backend, the callback is being evaluated for every instance of a subscriber.

calculating the derived store, attempt 1
calculating the derived store, attempt 2
calculating the derived store, attempt 3
calculating the derived store, attempt 4

Compare those console logs with those seen on the browser, which I would consider to be the correct behavior given the documentation, where there is only a single evaluation, at the time of the first subscription:

calculating the derived store, attempt 1

What else did I try?

• This happens even if the store is a singleton in some other ts file
• This happens if the store is passed via context as opposed to exports