subscriptions are lost during HMR

[duoyue]

I have some code like this , it could output correctly when app first loaded or refresh ，but don‘t work after HMR.

const pinia = createPinia();
pinia.use(({ store }) => {
  store.$subscribe((mutations, state) => {
    console.log('trigger subscritions ', mutations, state);
  });
});

I have add some breakpoints in Pinia.js ，and found that subscriptions is emty [] after HMR.

// the  "subscriptions" is empty [] after HMR
function triggerSubscriptions(subscriptions, ...args) {
    subscriptions.forEach((callback) => {
        callback(...args);
    });
}

[posva]

Maybe this can be fixed but it does require some extra logic because any subscription that happens inside a plugin should not be transferred. There could be other cases of subscriptions that should not be transferred to avoid duplication.

Or maybe there is even a better solution within acceptHMRUpdate

[davidmyersdev]

@posva what do you mean by "any subscription that happens inside a plugin should not be transferred" here? I'm also running into this problem when trying to develop a plugin locally. The plugin only receives the $subscribe callback once before it is removed. Hot-reloading for plugins seems difficult since the initial plugin registration can have side effects on the current store state (e.g. hydrating the state from localStorage).

[davidmyersdev]

Additionally, it looks like this problem goes away when using detached: true by preventing the removeSubscription callback from firing on unmount. Is that configuration expected for plugins that need to subscribe to mutations/actions?

[Alanscut]

Passing { detached: true } as the second parameter seems to fix this.

[emrysctl]

thanks

[posva]

Additionally, it looks like this problem goes away when using detached: true by preventing the removeSubscription callback from firing on unmount. Is that configuration expected for plugins that need to subscribe to mutations/actions?

yes: in most cases you want to use detached: true in plugins so the subscription is never removed

[F0rsaken]

I think it would be very useful to mention it in plugins section of docs, especially in the $subscribe section as if you develop a plugin and use $subscribe or $onAction, you almost certainly want to use detach: true

[posva]

@F0rsaken Totally! Could you do a PR?

[F0rsaken]

@posva sure, created PR with docs update #1781 👍