Nuxt•6d ago

Hydration and caching issues on universal rendering page

I have three issues on a page that is using SSR / universal rendering... 1. There are hydration errors — I'm guessing this is something I've misconfigured in the client-side code. Page code: https://github.com/seancdavis/qr-polls/blob/main/pages/polls/%5Bid%5D.vue 2. I'm curious why the initial response is empty. The docs noted that universal rendering had the benefit of SEO/prerendering + hydration, but maybe I'm thinking about this wrong?

<body>
  <div id="__nuxt">
    <div>
      <!---->
    </div>
  </div>
  <!---->
</body>

<body>
  <div id="__nuxt">
    <div>
      <!---->
    </div>
  </div>
  <!---->
</body>

3. I don't seem to be able to set response headers from that dynamic page. They worked when specified in the config file, but I need to set at least one of them dynamically from the page. Relevant code: https://github.com/seancdavis/qr-polls/blob/main/pages/polls/%5Bid%5D.vue#L8-L13 Code: https://github.com/seancdavis/qr-polls Demo: https://qr-polls.netlify.app/ Netlify cache inspector: https://cache-inspector.netlify.app/

GitHub

qr-polls/pages/polls/[id].vue at main · seancdavis/qr-polls

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GitHub

GitHub - seancdavis/qr-polls

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8 Replies

kapa.ai•6d ago

Hi @seancdavis. 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 knowledge sources provided and your question, I'll address each of your issues: 1. Hydration errors: Hydration errors can occur when there's a mismatch between the server-rendered content and the client-side rendered content. This is a common issue in universal rendering. Vue 3.4 has improved the debugging of hydration errors, making them easier to identify and fix. YouTube [Nuxt 3]: The new Vue 3.4 feature NOBODY talks about… (+ raffle) mentions this improvement. To debug your specific case, you should check for any data that might be different between server and client rendering. This could be due to API calls, date/time functions, or any other dynamic content. Make sure that your data fetching is consistent between server and client. 2. Empty initial response: The empty initial response you're seeing might be due to how Nuxt handles universal rendering. Nuxt uses a two-step process: first, it renders on the server, then it hydrates on the client. The empty <div> you're seeing could be a placeholder that Nuxt uses before the content is fully rendered and hydrated. However, if you're not seeing any content at all, even after the page loads, there might be an issue with your data fetching or rendering logic. Make sure you're using Nuxt's data fetching methods like useFetch or useAsyncData correctly, as these ensure proper handling of data during server-side rendering and client-side hydration. Docs > Getting-started > Data Fetching provides information on how to properly fetch data in Nuxt applications. 3. Setting response headers dynamically: For setting response headers dynamically from a page, you can use the useResponseHeader composable. This is available in Nuxt v3.14+. Here's how you can use it:

const header = useResponseHeader('X-My-Header');
header.value = 'my-value';

const header = useResponseHeader('X-My-Header');
header.value = 'my-value';

Docs > Api > Composables > useResponseHeader provides more details on this. If you're using an older version of Nuxt, you might need to update to use this feature. Alternatively, you could explore using a server middleware to set headers dynamically. It's worth noting that setting headers might not work as expected when deploying to certain platforms that use edge caching, like Netlify. In such cases, you might need to configure your deployment platform to respect these headers. For more detailed debugging and solutions, you might want to check the Nuxt DevTools, as mentioned in Docs > Getting-started > Data Fetching, which can help inspect the payload and identify issues with data fetching and rendering. ---------------------- Note: you can ask me a follow up question by @ mentioning me again :speech_balloon: ----------------------

kapa.ai•6d ago

<@620932932605050890> Kapa.ai is still learning and improving, please let me know how I did by reacting below.

manniL•6d ago

@seancdavis 1 and 2 might be related (possibly 3 too) I'd probably try building locally yarn build, then whatever run command (usually node .output/and/so/on) to see if it is an issue locally as well. If the hydration warnings don't appear locally (after refreshing the polls page), you can also build with debug: true to get better hydration warnings, which should tell you exact elements.

seancdavisOP•6d ago

@TheAlexLichter Ahhh, okay. Progress... After yarn build, I can preview with node .output/server/index.mjs. I don't get a hydration error and I see content in the initial response:

<body>
  <div id="__nuxt">
    <div>
      <div
        class="bg-gradient-to-b from-slate-800 to-slate-950 min-h-screen text-white"
      >
        <header></header>
        <main class="max-w-5xl mx-auto px-8 py-8">
          <div class="mb-16 pt-12 text-center">
            <h1 class="text-3xl sm:text-4xl font-bold tracking-tight">
              Is this an example question?
            </h1>
          </div>
          <!-- ... -->
        </main>
        <footer></footer>
      </div>
    </div>
  </div>
  <!-- ... -->
</body>

<body>
  <div id="__nuxt">
    <div>
      <div
        class="bg-gradient-to-b from-slate-800 to-slate-950 min-h-screen text-white"
      >
        <header></header>
        <main class="max-w-5xl mx-auto px-8 py-8">
          <div class="mb-16 pt-12 text-center">
            <h1 class="text-3xl sm:text-4xl font-bold tracking-tight">
              Is this an example question?
            </h1>
          </div>
          <!-- ... -->
        </main>
        <footer></footer>
      </div>
    </div>
  </div>
  <!-- ... -->
</body>

I then ran netlify build to see what the difference is, and I noticed that the adapter puts everything in dist, doing all the transformations in the process. Does that make it seem like #1 and #2 are Netlify adapter issues? --- In addition, the Netlify adapter adds a _headers file and I noticed that it doesn't pick up the redirects mentioned in the page file (src/pages/polls/[id].vue). Going to check with the team on that one.

manniL•6d ago

I then ran netlify build to see what the difference is, and I noticed that the adapter puts everything in dist, doing all the transformations in the process.

If you run the build command with a set preset (e.g. configured via nitro.preset or the env variables) that should also do the necessary transforms for netlify

Config - Nitro

Philippe Serhal•6d ago

FYI it uses the netlify preset automatically when it detects that it's running via the Netlify CLI

I noticed that it doesn't pick up the redirects mentioned in the page file (src/pages/polls/[id].vue)

🤔 was redirects here a typo for headers? The generated _headers file will only contain statically configured headers (i.e. from routeRules), not anything dynamically set in runtime code I'm not familiar with nuxt rendering internals, but I'm suspicious of this:

setInterval(refresh, 1000);

setInterval(refresh, 1000);

Wouldn't this run on the server as well? Maybe nuxt SSR somehow keeps track of background work and this trips it up?

seancdavisOP•5d ago

Yes. I meant headers. That makes sense. The others should be generated at runtime and get moved to the serverless SSR function. I was trying to show that by running with and without --preset netlify is that the behavior of the /polls/[id] route is different. Not sure exactly how Nuxt resolves what runs on server vs client. Can you share more about that, @manniL ?

Philippe Serhal•5d ago

It's pretty well documented here: https://nuxt.com/docs/guide/concepts/nuxt-lifecycle. AFAIK the setup script runs entirely on both (in universal rendering mode). There are specific components/composables/utils that only run on the server (e.g. https://nuxt.com/docs/api/utils/set-response-status) or on the browser (https://nuxt.com/docs/api/components/client-only) and there's the https://nuxt.com/docs/api/utils/call-once util to wrap an arbitrary piece of code to run on the server only.

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Hydration and caching issues on universal rendering page

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