How can I synchronize two stores without running into an infinite loop?

The following code triggers an infinite loop:

const [store1, setStore1] = createStore({a: 1, b: 2});
const [store2, setStore2] = createStore();

createEffect(() => {
  setStore1(store2);
});

createEffect(() => {
  setStore2(store1);
});

const [store1, setStore1] = createStore({a: 1, b: 2});
const [store2, setStore2] = createStore();

createEffect(() => {
  setStore1(store2);
});

createEffect(() => {
  setStore2(store1);
});

How can I update one when the other changes and avoid this?

6 Replies

mrVinicius•8mo ago

what is the actual use case behind this?

DittoOP•8mo ago

I'm using felte (https://felte.dev/docs) for form state management, but I want to have a copy of the form's values higher in the component hierarchy so that I can keep the state between mounts/unmounts.

Felte | Documentation

An extensible form library for Svelte, Solid and React.

DittoOP•8mo ago

So my idea was: copy felte's data store whenever it changes to another store and restore it's state using the cached one when it mounts again. I could just move the createForm call to a parent component, but then it would be far away from where it is actually used.

mrVinicius•8mo ago

it seems the form is the source of truth, why don't have a single createEffect?

DittoOP•8mo ago

How would that work? I want to 1. Cache form state when it changes. 2. Restore form state when it remounts using the cached form state.

mrVinicius•8mo ago

what i can think of is the data should flow from the form store to cache store, and when mounting again you could emit a single set operation to put the data back into the form. one createEffect to keep your cache fresh as the form gets updated, and one onMount() put the data back in the form store

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How can I synchronize two stores without running into an infinite loop?