fix issue of persisting data on initial load.

[byteab]

WIP:

fixing the issue of #366

• issue
• test
• code review

src/middleware
line 277:286

         if (migratedState) {
           set(migratedState)
           await setItem()
        }    
+     } else {
+        await storage.setItem(name, await serialize({...get() || {}}) 
+     }

[dai-shi]

Thanks for your work.
At this point, I'm not sure what issue you are trying to solve.
For #366, my suggestion is firstly to fix the async issue #366 (comment) which allows to fix the issue on lib user end, and if we need better developer experience we can follow up. (I prefer step by step.)

[dai-shi]

This seems another issue from what I think we should fix firstly, but I am not sure if this is desired. At least I don't want to write to localStorage without change. I think this should be optional, and if async issues are solved, there's a workaround, and we will see what we want.

[byteab]

the initial value of the store shouldn't be written in localStorage? Do you mean this?

for example

const useStore = create((set) => ({
     friends: 10,
     setFriends: () => set({friends: 20})
}, {name: "my-storage"}))

so the localStorage will not store the value friends: 10, until you update the value by setFriends

here is a sandbox that replicate it:
https://codesandbox.io/s/zustand-persist-debug-0k6ui?file=/src/App.js

[dai-shi]

Right, in my use case in mind, I wouldn't store the default value.

const useStore = create(persist((set) => ({
     userName: "No Name",
     setUserName: (userName) => set({ userName })
}), { name: "my-user-setting" }))

In this case, I don't want to store "No Name" in localStorage.

[dai-shi]

Hm, and your use case of storing default value seems already covered by postRehydrationCallback. So, it's already supported, I'd say.

https://codesandbox.io/s/zustand-persist-debug-forked-bi4nr?file=/src/App.js
Not super pretty, but it works.
(The issue it doesn't show on the screen is another issue, which I refer as the first issue.)

[byteab]

storing default value is optional. and if someone wants to store, it should use the postRehydrationCallback callback.
Ok, I got it.