N
Nuxt•4w ago
kāné

Nuxt 3 API Endpoint Data Lost During Server-Client Transfer Despite Valid Server-Side Data

I'm experiencing a puzzling issue with my Nuxt 3 application where data is being lost during the transfer from server to client, despite the data being valid on the server side. Setup I have a view model that handles data transformation: 
class ItemViewModel {
  // ... other properties and methods

  toJSON() {
    return {
      id: this.id,
      title: this.title,
      description: this.description,
      // ... other properties
    };
  }
}
class ItemViewModel {
  // ... other properties and methods

  toJSON() {
    return {
      id: this.id,
      title: this.title,
      description: this.description,
      // ... other properties
    };
  }
}
And an API endpoint that returns this data: 
// server/api/items/[id].get.ts
export default defineEventHandler(async (event) => {
  const id = getRouterParam(event, 'id');
  const result = await MyService.getItem(id);
  const item = ItemViewModel.fromData(result);
  
  // Server-side console shows this data is valid
  console.debug('item.toJSON():', item.toJSON());  // Shows correct data structure
  
  return item.toJSON();
});
// server/api/items/[id].get.ts
export default defineEventHandler(async (event) => {
  const id = getRouterParam(event, 'id');
  const result = await MyService.getItem(id);
  const item = ItemViewModel.fromData(result);
  
  // Server-side console shows this data is valid
  console.debug('item.toJSON():', item.toJSON());  // Shows correct data structure
  
  return item.toJSON();
});
On the client side, I'm fetching the data: 
<script setup>
const route = useRoute();
const { data, pending, error } = await useFetch(`/api/items/${route.params.id}`);

// data.value is null, despite server logs showing valid data
console.log('Client data:', data.value);  // null
</script>
<script setup>
const route = useRoute();
const { data, pending, error } = await useFetch(`/api/items/${route.params.id}`);

// data.value is null, despite server logs showing valid data
console.log('Client data:', data.value);  // null
</script>
The Weird Part * The server-side logs show the data is valid and structured correctly * If I explicitly return a plain object with the same properties within the API endpoint, instead of return item.toJSON() it works: 
// server/api/items/[id].get.ts
...
// This works
return {
  id: item.toJSON().id,
  title: item.toJSON().title,
  description: item.toJSON().description
};
// server/api/items/[id].get.ts
...
// This works
return {
  id: item.toJSON().id,
  title: item.toJSON().title,
  description: item.toJSON().description
};
* Returning item.toJSON() results in a null response on the client side * I've tried various serialization approaches (superjson, JSON.stringify/parse) but the issue persists What's going on here? Why does explicitly creating a new object work while returning the toJSON() result doesn't? Is there something about Nuxt's serialization that I'm missing?
2 Replies
kapa.ai
kapa.ai•4w ago
Hi @kāné. I'm kapa.ai, your friendly support bot. I will try to answer your question by searching through the knowledge base. :wave: ---------------------- Based on the information provided in the knowledge sources, I can offer some insights into your issue with Nuxt 3 data serialization during server-to-client transfer. This problem appears to be related to how Nuxt handles complex data types and serialization. The root cause of your issue likely stems from how Nuxt serializes data when transferring it from the server to the client. Nuxt uses a specific serialization process to ensure that data can be safely transferred and rehydrated on the client side. Here are some key points to consider: 1. Serialization Process: Nuxt uses devalue (https://github.com/Rich-Harris/devalue) for serializing data from server to client. This allows for transferring more complex data types beyond basic JSON. Docs > Getting-started > Data Fetching > Serializing Data From Server to Client (https://nuxt.com/docs/getting-started/data-fetching#serializing-data-from-server-to-client) 2. Custom Class Serialization: When using custom classes (like your ItemViewModel), you may need to define a custom serializer/deserializer. Nuxt doesn't automatically know how to handle custom class instances. Docs > Api > Composables > useNuxtApp > payload (https://nuxt.com/docs/api/composables/use-nuxt-app#payload) 3. API Route Serialization: For data returned from API routes (like your /api/items/**id].get.ts), Nuxt uses JSON.stringify for serialization, which has limitations with custom classes. [Docs > Getting-started > Data Fetching > Serializing Data From API Routes (https://nuxt.com/docs/getting-started/data-fetching#serializing-data-from-api-routes) To resolve your issue, you have a few options: 1. Use a Custom Serializer: Define a custom serializer for your ItemViewModel class. You can do this using a payload plugin: 
   // plugins/item-view-model-payload.ts
   export default definePayloadPlugin((nuxtApp) => {
     definePayloadReducer('ItemViewModel', (value) => {
       return value instanceof ItemViewModel && value.toJSON()
     })
     definePayloadReviver('ItemViewModel', (value) => {
       return ItemViewModel.fromJSON(value)
     })
   })
   
   // plugins/item-view-model-payload.ts
   export default definePayloadPlugin((nuxtApp) => {
     definePayloadReducer('ItemViewModel', (value) => {
       return value instanceof ItemViewModel && value.toJSON()
     })
     definePayloadReviver('ItemViewModel', (value) => {
       return ItemViewModel.fromJSON(value)
     })
   })
2. Return Plain Objects: As you've discovered, returning plain objects works. This is because Nuxt can easily serialize plain objects. You can modify your API endpoint to always return plain objects: 
   return {
     id: item.id,
     title: item.title,
     description: item.description
     // ... other properties
   };
   
   return {
     id: item.id,
     title: item.title,
     description: item.description
     // ... other properties
   };
3. Use toJSON Method: If you prefer to keep using the toJSON method, ensure that it's returning a plain object and not any custom class instances: 
   class ItemViewModel {
     toJSON() {
       return {
         id: this.id,
         title: this.title,
         description: this.description,
         // ... other properties
       };
     }
   }
   
   class ItemViewModel {
     toJSON() {
       return {
         id: this.id,
         title: this.title,
         description: this.description,
         // ... other properties
       };
     }
   }
Then in your API endpoint: 
   return item.toJSON();
   
   return item.toJSON();
By implementing one of these solutions, you should be able to resolve the serialization issue and successfully transfer your data from server to client. For more detailed information on payload serialization in Nuxt 3, you can refer to Docs > Api > Composables > useNuxtApp > payload** (https://nuxt.com/docs/api/composables/use-nuxt-app#payload) and watch the video by Alexander Lichter mentioned in the documentation about serializing payloads, especially with regards to classes. ---------------------- Note: you can ask me a follow up question by @ mentioning me again :speech_balloon: ----------------------
kapa.ai
kapa.ai•4w ago
<@308827449213452289> Kapa.ai is still learning and improving, please let me know how I did by reacting below.

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