fix: Vuex mutation error when using useFetch

[aaronhuisinga]

🐛 The bug
In some instances using Vuex with useFetch can result in the following error: [vuex] do not mutate vuex store state outside mutation handlers..

It appears that having an object with a value set to either an array or an object is enough to trigger this error. Any simple data type or an object containing only simple data types (strings, numbers, etc) will not trigger it.

This only occurs when manipulating the store item within a useFetch call, and returning the computed property from the setup method.

Example that will not cause issue:

{ id: 11, name: 'Test Person' }

Example that will cause issue:

{ id: 11, roles: [1, 2] }

🛠️ To reproduce
Steps to reproduce the behavior:

1. Setup Vuex store, page, and Nuxt Composition API
2. Set item from Vuex store to computed property, and return from setup method.
3. Manipulate the item in the Vuex store within a useFetch method. The item must be an object, and have a property set to either an object or array.

Reproduction: https://stackblitz.com/edit/nuxt-starter-vylpg5?devtoolsheight=33&file=pages%2Findex.vue

🌈 Expected behaviour
The expected behavior is for the item to not be mutated outside of mutation handlers, and successfully render.

[aaronhuisinga]

@danielroe It appears this issue started with v0.28.0. My guess is it's due to #541.

[Dell-it]

@aaronhuisinga Hello, I met with the same problem, did you manage to solve/work around it somehow?

[aaronhuisinga]

@aaronhuisinga Hello, I met with the same problem, did you manage to solve/work around it somehow?

For the time being I've just locked the package at v0.27.0. That has all of the functionality I need anyway and works as expected.

You could also start the upgrade to Nuxt 3 using Nuxt Bridge. There is quite a bit of work to do if you've been using this package, and I'm not sure how stable it is, so proceed at your own risk there. I started the process for one of the Nuxt apps I maintain, but decided to wait until more functionality was implemented before continuing.

[adrianwix]

I faced the same issue and it was driving me insane. This needs an urgent fix

[adrianwix]

@danielroe Any update on it? Not being able to update the store inside useFetch is messing up all the business logic in my app. If I use onMounted I get a bunch of server-side errors in other components. If I use composables I have to fetch the same entity every single time.

I won't migrate to nuxt-bridge until it is stable

[danielroe]

You should not manipulate the store within useFetch. Instead use useAsync, which does not stringify the entire component state.

[janvacek]

@danielroe ok, but if you use useAsync, it will be called twice - server side and then client side - or not?

[danielroe]

No, it will not.

[janvacek]

@danielroe look at this issue, I have the same problem with useAsync #652, thats why I wrote my last comment, it is called twice even with simple example

[adrianwix]

@danielroe One question how do you use useAsync then to fetch data where you have 2 API calls and the second call depends on the first one? What my team end up doing is the following

const user = ref()
const documents = ref()
/**
* fetchUser and fetchDocument are defined here and set the values above
*/
async function initiateMethods() {
            user = await fetchUser()
            documents = await fetchDocuments()
}
useAsync(() => initiateMethods())

in this the right way? from my understanding if useAsync is analogous to asyncData it should be something like

async function initiateMethods() {
            const user = await fetchUser()
            const documents = await fetchDocuments(user.id)
            return { user, documents }
}

// here user and documents should be both reactive references. But since asyncData returns only one reactive object
const { user, documents } = useAsync(() => initiateMethods())

// should we do this?
const data = useAsync(() => initiateMethods())
const user = ref(data?.user || null)
const documents = ref(data?.documents || null)

I am asking here because we face these doubts because of the error mentioned in this thread. I think it is not clear enough how to use it in the nuxt composition plugin and sadly Nuxt/Vue 3 ecosystem needs like 6 more months to be usable (e.g Vuetify 3 is not yet ready for Vue 3)