feat: prevent race condition dev-only error

[meihao550]

What kind of change does this PR introduce?

Bug fix.

Did you add tests for your changes?

No. Reliably reproducing the null state inside @vue/test-utils + happy-dom requires an SSR/hydration timing race that does not occur in the current test harness. The fix is a one-line defensive null check that has no impact when instance is already defined, so a regression test would only exercise the untouched code path. Happy to add one if a reviewer can suggest a stable reproduction pattern.

If relevant, did you update the documentation?

No documentation change needed.

Summary

Under certain rendering conditions — observed in a Nuxt 4 SSR app with @nuxt/content — component.ref.i in RouterView.ts is null when the dev-only devtools branch runs. The unguarded instance.__vrv_devtools = info assignment then throws:

TypeError: null is not an object (evaluating 'instance.__vrv_devtools = info')

crashing the app on first render.

Change

 internalInstances.forEach(instance => {
   // @ts-expect-error
-  instance.__vrv_devtools = info
+  if (instance) instance.__vrv_devtools = info
 })

Why this is safe

• The block is guarded by __DEV__ || __FEATURE_PROD_DEVTOOLS__ and isBrowser, so production builds are unaffected.
• When instance is truthy the behavior is unchanged.
• When instance is null, the devtools info is simply not attached to that entry. RouterView re-runs this code on subsequent renders / re-mounts, so no persistent state is lost.

Reproduction steps

1. Create a fresh Nuxt 4 project.
2. Install @nuxt/content (v3.15.2) and register it in nuxt.config.ts:

   export default defineNuxtConfig({
     modules: ['@nuxt/content']
   })

3. Add a minimal page app/pages/index.vue:

   <template><div>hello</div></template>

4. Run npm run dev and open http://localhost:3000.
5. The page renders briefly, then the app crashes with the TypeError shown above.

Environment: Nuxt 4.5.2, @nuxt/content 3.15.2, vue-router 5.2.0, Vue 3.5.41.

---

Non-native English speaker; apologies for any awkward phrasing.

Summary by CodeRabbit

• Bug Fixes
  • Improved devtools metadata handling to prevent errors when an internal component instance is unavailable.
  • Added safeguards for potential server-side rendering timing conditions.

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📥 Commits

Reviewing files that changed from the base of the PR and between 89161b8 and 7edaf93.

📒 Files selected for processing (1)

• packages/router/src/RouterView.ts

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• packages/router/src/RouterView.ts

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---

📝 Walkthrough

Walkthrough

RouterView now guards the __vrv_devtools metadata assignment when the internal component instance is undefined. The change also documents a possible SSR race condition.

Changes

RouterView devtools metadata

Layer / File(s)	Summary
Guard devtools metadata assignment packages/router/src/RouterView.ts	The __vrv_devtools metadata assignment now runs only when the internal component instance exists. The code documents a possible SSR race condition.

Estimated code review effort: 1 (Trivial) | ~3 minutes

Merge Risk: ⚪ Minimal · up to 7edaf

The PR adds a localized null guard in a dev-only RouterView path, preventing a first-render crash when an instance is absent while preserving existing behavior for valid instances; no actionable merge-blocking risk remains after normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the dev-only crash prevention caused by a race condition in the changed RouterView path.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[posva]

The fix is fine indeed but sounds like another bug worth digging. Do you have a repro without nuxt?

[pkg-pr-new]

Open in StackBlitz

pnpm add https://pkg.pr.new/vue-router@2789

npm i https://pkg.pr.new/vue-router@2789

yarn add https://pkg.pr.new/vue-router@2789.tgz

commit: 7edaf93

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.95%. Comparing base (67babd4) to head (7edaf93).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2789   +/-   ##
=======================================
  Coverage   85.95%   85.95%           
=======================================
  Files          74       74           
  Lines        5895     5895           
  Branches     1893     1894    +1     
=======================================
  Hits         5067     5067           
  Misses        732      732           
  Partials       96       96           

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[meihao550]

The fix is fine indeed but sounds like another bug worth digging. Do you have a repro without nuxt?

Thanks for your reply

At the moment, I have only been able to reproduce it in a Nuxt 4 + @nuxt/content setup. I haven't yet found a reliable reproduction using vue-router alone.
My current suspicion is that this is related to an SSR/hydration timing issue, since component.ref.i appears to be null during the devtools registration path, but I don't yet have enough evidence to say whether the root cause is in vue-router, Vue itself, or an interaction with Nuxt/@nuxt-content.

[meihao550]

This is the bug caused by bug in the nuxt project
I thought It was a Vue router Issue So That's why I mentioned it