Component styles flicker/blink with SSR mode on

[Destaq]

Describe the bug

When applying stylings to components or pages, on SSR mode, first server stylings get rendered, and then client ones.

In some cases, when components / pages use more 'dynamic' data like slots, $$restProps with class names, lists, etc., what oddly happens is that there is a 'flicker', where server stylings do not seem to match client ones.

Below is a video with two examples of when this happens:

https://github.com/sveltejs/kit/assets/61620873/e5688342-1c23-4994-a4ba-807fc1247e1b

Reproduction

About twenty lines: https://www.sveltelab.dev/vg1t4x2cb8n84f4

Logs

No response

System Info

I've spoken to a number of people so I don't think that it is a device-specific thing. But anyway:


  System:
    OS: macOS 13.3.1
    CPU: (8) arm64 Apple M1
    Memory: 83.23 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 19.6.0 - /opt/homebrew/bin/node
    Yarn: 1.22.11 - /opt/homebrew/bin/yarn
    npm: 9.4.0 - /opt/homebrew/bin/npm
  Browsers:
    Brave Browser: 113.1.51.114
    Safari: 16.4
  npmPackages:
    @sveltejs/adapter-auto: ^1.0.0-next.91 => 1.0.0-next.91 
    @sveltejs/kit: next => 1.0.0-next.589 
    svelte: ^3.55.1 => 3.55.1 
    vite: ^4.0.0 => 4.1.1 

Severity

annoyance

Additional Information

No response

[Destaq]

The same issue happens even when setting export const csr = false. Interestingly, the only workaround seems to be wrapping for loops in a flexbox.

<div style="display:flex;">
   {#each item as item}
       <!-- represent the item details in a tailwind card -->
       <div class="w-64 inline-block bg-pink">
           <div>
               <a href="/media/{item}">Page</a>
           </div>
       </div>
   {/each}
</div>

But I would suggest this approach be avoided. When setting e.g. 5 divs (without the for loop), there are no spaces. Only through the above do they have spaces on the server-rendered HTML, and then revert to no spaces / gaps as expected (see repro). So this seems to be more of a workaround than expected behavior.

[geoffrich]

This issue is not caused by when styles are applied, but differences in the whitespace present in the SSR markup and the client-side rendered elements.

The SSR markup inserts a text node with "\n " between each child div:

But when client-side rendered, those nodes are removed:

There are multiple whitespace issues open in the Svelte repo, so not sure if this is a duplicate or not (or what workarounds would be). Transferring over there for now.

[ryanatkn]

I've looked through the issues and I don't see an exact duplicate.

If it wasn't clear from the OP, if you don't need SSR, disabling it avoids the issue:

// +layout.ts
export const ssr = false;