since 2.21.3 navigating causes error in bundle.js and forces page reload

[timotejroiko]

Describe the bug

Since installing 2.21.3 every navigation forces a page reload and shows this in the browser console:

bundle.CUuEHxTC.js:3 Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'decoders')

inspecting the above file after prettifying it in dev tools points to this:

Ma(["click"]);
const Xd = De.decoders; // <-error here
function eg(e) {
    const r = JSON.parse(e);
    return r.data && (r.data = j_(r.data, Xd)),
    r
}

After playing around with configuration and adding/removing things, i was not able to determine exactly which part of the project triggers it, i simply decided to rollback to 2.21.2

Is this a known issue or is there any specific configuration group i should look into to try and find a root cause?

Also, the issue seems to happen only in production, it does not occur in dev mode.

Also, it seems client-side JS completely stopped functioning.

Reproduction

I was not able to determine exactly which part of my project causes it.

Logs

System Info

System:
    OS: Linux 6.1 Debian GNU/Linux 12 (bookworm) 12 (bookworm)
    CPU: (2) x64 AMD EPYC Processor
    Memory: 845.43 MB / 1.87 GB
    Container: Yes
    Shell: 5.2.15 - /bin/bash
  Binaries:
    Node: 24.0.2 - ~/.nvm/versions/node/v24.0.2/bin/node
    npm: 11.3.0 - ~/.nvm/versions/node/v24.0.2/bin/npm
  npmPackages:
    @sveltejs/adapter-node: 5.2.12 => 5.2.12 
    @sveltejs/enhanced-img: 0.6.0 => 0.6.0 
    @sveltejs/kit: ^2.21.3 => 2.21.3 
    @sveltejs/vite-plugin-svelte: 5.1.0 => 5.1.0 
    svelte: 5.33.18 => 5.33.18 
    vite: 6.3.5 => 6.3.5

Severity

blocking an upgrade

Additional Information

No response

[kposborne]

I run unit tests with jsdom, they started failing with this error upon attempting to upgrade to 2.21.3. Based on the error message, it looks related to this change: #13686

TypeError: Cannot read properties of undefined (reading 'decoders')
 ❯ node_modules/@sveltejs/kit/src/runtime/app/forms.js:9:39
      7| export { applyAction };
      8| 
      9| const decoders = BROWSER ? client_app.decoders : server_app?.decoders;
       |                                       ^
     10| 
     11| /**
 ❯ node_modules/sveltekit-superforms/dist/client/superForm.js:11:1

[bigmac44]

I run unit tests with jsdom, they started failing with this error upon attempting to upgrade to 2.21.3. Based on the error message, it looks related to this change: #13686

Same error with vitest browser tests. Error with 2.21.3 but not 2.21.2.

[eltigerchino]

Managed to reproduce this. The conditions are building an single/inline output app which causes app to not get initialised before the following statement is evaluated (as Elliot pointed out)

kit/packages/kit/src/runtime/app/forms.js

Line 9 in 73cc8a5

const decoders = BROWSER ? client_app.decoders : server_app?.decoders;

Fortunately, we can move this away from the top-level and it still gets tree-shaken for server/client.