persistState with localStorageStrategy

[SatarisGIT]

Hello!

I'd like to inquire about using persistState with localStorageStrategy as outlined here -> https://ngneat.github.io/elf/docs/features/persist-state/

How might I employ it to filter or manipulate the saved localStorageEntities whenever my model undergoes a change, and I aim to "migrate" it to a newer format? My localStorage harbors old data, lacking some keys, which exposes me to the risk of type errors. I wish to manually filter and verify everything comprehensively.

Currently, I am utilizing the "source" method as a persistState option, albeit not with a straightforward store.update, but with an appended setTimeout with a 0 timeout value. Absent the setTimeout, the state operates fine, values are altered but solely during runtime, without any preservation in localStorage.

In my scenario, "preStoreInit" doesn't seem to effect any changes, regardless of whether I alter or remove something. I'm uncertain about its function aside from some side logic somewhere. I fail to grasp why it necessitates the return of the store as a value, given it doesn't alter anything at all.

Are there superior alternatives? What exactly is the intent behind "preStoreInit"?

[johnfewell]

Can you post the function you provide for preStoreInit? There isn't a test in the repo, but I just wrote one, and it passed by successfully transforming the state.

[SatarisGIT]

This is it:

`export const persist = persistState(settingsStore, {
key: 'settings',
storage: localStorageStrategy,

preStoreInit(value) {
	console.warn('preStoreInit', value);

	setTimeout(() => {
		settingsStore.update(setSettings(defaultSettings));
	}, 0);

	return { settings: defaultSettings } as Partial<{
		settings: ISettings;
	}>;
},

source: (store) => {
	return store;
},

});`

without this "setTimeout" this is not working.
Problem occurs only when 'storage: localStorageStrategy' is used

[johnfewell]

Why are you calling settingsStore.update() from inside preStoreInit? Why not return the default setting directly in preStoreInit? Something like:

export const persist = persistState(settingsStore, {
  key: 'settings',
  storage: localStorageStrategy,
  preStoreInit(value) {
    return { settings: defaultSettings } as Partial<{
      settings: ISettings;
    }>;
  },
  source: (store) => {
    return store;
  },
});

preStorageInit isn't documented, but preStorageUpdate is. It works the same way as preStorageInit, but it runs before the state is saved rather than when it's retrieved.

[SatarisGIT]

preStorageUpdate will run everytime when I change value of store, in my case I want to simply check that already saved data in localStorage is assignable to type interface - only one time, at start.

If type is invalid - I want to "repair" it by migrate settings from different versions.