Nuxt•3d ago

Set ref in useAsyncData

in nuxt2 with the @nuxtjs/composition-api plugin i was able to do this:

const foo = ref(null)

useFetch(() => {
   const data = await fetchData()

   foo.value = data
})

const foo = ref(null)

useFetch(() => {
   const data = await fetchData()

   foo.value = data
})

is there a way to set some refs inside setup when fetching in nuxt 3? or do i have to refactor all of my useFetch usages?

13 Replies

kapa.ai•3d ago

Hi @grip. I'm kapa.ai, your friendly support bot. I will try to answer your question by searching through the knowledge base. :wave: ---------------------- In Nuxt 3, the behavior of useFetch and useAsyncData has changed compared to Nuxt 2 with the @nuxtjs/composition-api plugin. The approach you were using in Nuxt 2 is not directly applicable in Nuxt 3. However, there are ways to achieve similar functionality in Nuxt 3 without having to completely refactor all your useFetch usages. Here's how you can approach this in Nuxt 3: 1. Use the transform option: You can use the transform option of useAsyncData or useFetch to modify the data before it's assigned to the data ref:

const foo = ref(null)

const { data } = await useAsyncData('key', () => fetchData(), {
  transform: (fetchedData) => {
    foo.value = fetchedData
    return fetchedData
  }
})

const foo = ref(null)

const { data } = await useAsyncData('key', () => fetchData(), {
  transform: (fetchedData) => {
    foo.value = fetchedData
    return fetchedData
  }
})

2. Use the watch option: You can watch the data ref returned by useAsyncData or useFetch and update your custom ref when it changes:

const foo = ref(null)

const { data } = await useAsyncData('key', () => fetchData())

watch(data, (newData) => {
  if (newData) {
    foo.value = newData
  }
})

const foo = ref(null)

const { data } = await useAsyncData('key', () => fetchData())

watch(data, (newData) => {
  if (newData) {
    foo.value = newData
  }
})

3. Use a computed property: If you don't need to mutate the data, you can use a computed property:

const { data } = await useAsyncData('key', () => fetchData())

const foo = computed(() => data.value)

const { data } = await useAsyncData('key', () => fetchData())

const foo = computed(() => data.value)

These approaches allow you to maintain reactivity and work with the data fetched by useAsyncData or useFetch in a way that's similar to what you were doing in Nuxt 2. It's worth noting that in Nuxt 3, it's generally recommended to work directly with the data ref returned by useAsyncData or useFetch, as this ensures proper SSR handling and hydration. However, the methods above can help you transition your existing code more easily. For more detailed information on how useAsyncData and useFetch work in Nuxt 3, you can refer to the official Nuxt 3 documentation: - useAsyncData (https://nuxt.com/docs/api/composables/use-async-data) - useFetch (https://nuxt.com/docs/api/composables/use-fetch) These composables are designed to handle asynchronous data fetching in an SSR-friendly way, which is why their usage differs from the Nuxt 2 + composition API plugin approach. ---------------------- Note: you can ask me a follow up question by @ mentioning me again :speech_balloon: ----------------------

kapa.ai•3d ago

<@338369338409222146> Kapa.ai is still learning and improving, please let me know how I did by reacting below.

gripOP•3d ago

@kapa.ai the first option didnt work. the data is there on the server but not on the client

kapa.ai•3d ago

Let me check the knowledge base for you again. One moment! :books: ---------------------- I apologize for the confusion in my previous answer. Let's investigate why the data might be available on the server but not on the client. This issue often relates to how Nuxt handles data fetching and hydration between server and client. Based on the information from the Nuxt documentation on Data Fetching (https://nuxt.com/docs/getting-started/data-fetching), there are a few important points to consider: 1. Make sure you're awaiting useAsyncData:

   const { data } = await useAsyncData('key', () => fetchData(), {
     transform: (fetchedData) => {
       foo.value = fetchedData
       return fetchedData
     }
   })

   const { data } = await useAsyncData('key', () => fetchData(), {
     transform: (fetchedData) => {
       foo.value = fetchedData
       return fetchedData
     }
   })

2. If you're not using await, you need to handle the promise:

   const { data, pending } = useAsyncData('key', () => fetchData(), {
     transform: (fetchedData) => {
       foo.value = fetchedData
       return fetchedData
     }
   })

   const { data, pending } = useAsyncData('key', () => fetchData(), {
     transform: (fetchedData) => {
       foo.value = fetchedData
       return fetchedData
     }
   })

3. Check if you're accidentally preventing the data from being added to the payload. As mentioned in the Nuxt documentation (https://nuxt.com/docs/getting-started/data-fetching#options):

Both pick and transform don't prevent the unwanted data from being fetched initially. But they will prevent unwanted data from being added to the payload transferred from server to client.

4. Ensure that your fetchData function is accessible on both server and client sides. 5. If the issue persists, you might want to try using the server option to force server-side rendering:

   const { data } = await useAsyncData('key', () => fetchData(), {
     server: true,
     transform: (fetchedData) => {
       foo.value = fetchedData
       return fetchedData
     }
   })

   const { data } = await useAsyncData('key', () => fetchData(), {
     server: true,
     transform: (fetchedData) => {
       foo.value = fetchedData
       return fetchedData
     }
   })

If none of these solutions work, the problem might be more complex. In that case, you might need to provide more details about your specific implementation, including how you're using the data in your component and any relevant configuration settings. Remember, if you have not fetched data on the server (for example, with server: false), then the data will not be fetched until hydration completes. This means even if you await useAsyncData on the client side, data will remain null within <script setup>, as mentioned in the Nuxt documentation (https://nuxt.com/docs/api/composables/use-async-data#return-values). If you're still facing issues, you might want to consider opening an issue on the Nuxt GitHub repository (https://github.com/nuxt/nuxt) with a minimal reproduction of your problem. ---------------------- Note: you can ask me a follow up question by @ mentioning me again :speech_balloon: ----------------------

kapa.ai•3d ago

<@338369338409222146> Kapa.ai is still learning and improving, please let me know how I did by reacting below.

gripOP•3d ago

@kapa.ai why use transform for this task? i can set the variable directly in the body of the handler of the useAsyncData. the problem is that the data flashes when hydrating

kapa.ai•3d ago

Let me check the knowledge base for you again. One moment! :books: ---------------------- You're right, and I apologize for the confusion in my previous answers. You can indeed set the variable directly in the handler of useAsyncData. The transform option isn't necessary for this task. Regarding the issue of data flashing during hydration, this is a common challenge in server-side rendering (SSR) applications. In Nuxt 3, this behavior is related to how the framework handles hydration and data fetching. To address the flashing issue during hydration, you can consider the following approaches: 1. Use lazy option:
The lazy option in useAsyncData can help prevent the flashing effect by resolving the async function after loading the route, instead of blocking client-side navigation. However, this might not be suitable if you need the data immediately.

   const { data } = await useAsyncData('key', 
     () => {
       const fetchedData = await fetchData()
       foo.value = fetchedData
       return fetchedData
     },
     { lazy: true }
   )

   const { data } = await useAsyncData('key', 
     () => {
       const fetchedData = await fetchData()
       foo.value = fetchedData
       return fetchedData
     },
     { lazy: true }
   )

2. Use <ClientOnly> component:
You can wrap the part of your template that uses the fetched data in a <ClientOnly> component. This will ensure that the content is only rendered on the client side, avoiding the hydration mismatch.

   <template>
     <ClientOnly>
       <!-- Content using fetched data -->
     </ClientOnly>
   </template>

   <template>
     <ClientOnly>
       <!-- Content using fetched data -->
     </ClientOnly>
   </template>

3. Check hydration state:
You can use nuxtApp.isHydrating to check if the app is currently hydrating and conditionally render content based on that. This approach is mentioned in the Nuxt documentation (https://nuxt.com/docs/api/composables/use-nuxt-app#ishydrating):

   <script setup>
   const nuxtApp = useNuxtApp()
   </script>

   <template>
     <div v-if="!nuxtApp.isHydrating">
       <!-- Content using fetched data -->
     </div>
   </template>

   <script setup>
   const nuxtApp = useNuxtApp()
   </script>

   <template>
     <div v-if="!nuxtApp.isHydrating">
       <!-- Content using fetched data -->
     </div>
   </template>

4. Use a loading state:
Implement a loading state that's shown while the data is being fetched or the app is hydrating. This can provide a smoother user experience.

   <script setup>
   const { data, pending } = useAsyncData('key', () => {
     const fetchedData = await fetchData()
     foo.value = fetchedData
     return fetchedData
   })
   </script>

   <template>
     <div v-if="pending">Loading...</div>
     <div v-else>
       <!-- Content using fetched data -->
     </div>
   </template>

   <script setup>
   const { data, pending } = useAsyncData('key', () => {
     const fetchedData = await fetchData()
     foo.value = fetchedData
     return fetchedData
   })
   </script>

   <template>
     <div v-if="pending">Loading...</div>
     <div v-else>
       <!-- Content using fetched data -->
     </div>
   </template>

These approaches can help mitigate the flashing effect during hydration. The best solution depends on your specific use case and the user experience you want to achieve. Nuxt Documentation (https://nuxt.com/docs/getting-started/data-fetching) provides more detailed information on data fetching and hydration in Nuxt 3. ---------------------- Note: you can ask me a follow up question by @ mentioning me again :speech_balloon: ----------------------

kapa.ai•3d ago

<@338369338409222146> Kapa.ai is still learning and improving, please let me know how I did by reacting below.

manniL•3d ago

you rather do const { data } = useAsyncData(async () => await fetchData()) (or straight away using useFetch if you want to use $fetch under the hood)

gripOP•3d ago

Ty Alex! Yes, I was just wondering if there is a way to avoid refactoring the data fetching logic everywhere in my app for now and do it after completing the migration but it seems like I don't have an option

manniL•3d ago

I mean, you could probably do a hacky refactoring but I wouldn't recommend that 😄 you could do:

const foo = ref(null)

useAsyncData(async () => {
   const data = await fetchData()

   foo.value = data
   return 1 // IMPORTANT TO AVOID REFETCHING
})

const foo = ref(null)

useAsyncData(async () => {
   const data = await fetchData()

   foo.value = data
   return 1 // IMPORTANT TO AVOID REFETCHING
})

this might break at any time in the future though as useAsyncData is not meant for side effects another option is:

const foo = ref(null)

callOnce(async () => {
   const data = await fetchData()

   foo.value = data
})

const foo = ref(null)

callOnce(async () => {
   const data = await fetchData()

   foo.value = data
})

This will only be called once (no refetching !)

gripOP•3d ago

Aha! I thought about callonce as well. I'll try both tomorrow. Awesome alex, thanks a lot! It's a huge app and I want to create the Nuxt 3 version with as minimal changes as possible and then start rennovating on a solid foundation

manniL•3d ago

No problem at all 👍
Hope it'll work out 🙏

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Set ref in useAsyncData