fix(angular-virtual): RuntimeError: NG0600: Writing to signals is not allowed in a computed or an effect by default by Stallion8472 · Pull Request #1109 · TanStack/virtual

Stallion8472 · 2026-01-05T19:28:45Z

🎯 Changes

Fixes #1096

✅ Checklist

I have followed the steps in the Contributing guide.
I have tested this code locally with pnpm run test:pr.

🚀 Release Impact

This change affects published code, and I have generated a changeset.
This change is docs/CI/dev-only (no release).

…puted or an effect by default by simplifying proxy

changeset-bot · 2026-01-05T19:28:49Z

🦋 Changeset detected

Latest commit: fae1553

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@tanstack/angular-virtual	Patch

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siddhant-dev · 2026-01-07T07:32:04Z

Any timeline for the release of this fix ?

piecyk · 2026-01-07T12:25:00Z

I’ll take a look at this soon, thanks!

lilianmisser-dg · 2026-02-19T14:42:29Z

Have you got more informations on when this pull request can be merged @piecyk ? 🙏

Copilot

Pull request overview

This PR addresses Angular runtime error NG0600 by changing how @tanstack/angular-virtual exposes reactive virtualizer state, aiming to avoid signal writes occurring during computed/effect evaluation.

Changes:

Removes the proxyVirtualizer-based implementation that created per-property computed signals on-demand.
Introduces a new Proxy wrapper around a single Virtualizer instance and exposes selected reactive properties via dedicated Angular signals updated from onChange.
Adds a changeset to release the fix as a patch for @tanstack/angular-virtual.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
packages/angular-virtual/src/proxy.ts	Removes the previous proxy-based lazy-init + computed-signal wrapping implementation.
packages/angular-virtual/src/index.ts	Reworks the adapter to use a concrete `Virtualizer` instance plus explicit Angular signals updated in `onChange`.
.changeset/clean-ends-wish.md	Declares a patch release for the Angular adapter fix.

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Copilot · 2026-03-12T19:03:39Z

packages/angular-virtual/src/index.ts

+        case 'options':
+          return options


options property on the returned AngularVirtualizer proxy is currently mapped to the input options signal rather than instance.options (the fully-normalized options object that Virtualizer actually uses). This changes runtime semantics and also diverges from AngularVirtualizer['options'] (which is typed as Signal<Virtualizer['options']>). Consider exposing a dedicated options signal that is updated from instance.options (e.g. in onChange and/or after setOptions) instead of returning the adapter’s options input signal here.

Copilot · 2026-03-12T19:03:39Z

packages/angular-virtual/src/index.ts

+          scrollRect.set(instance.scrollRect)
          _options.onChange?.(instance, sync)
        },
      })


The adapter signals (virtualItems, totalSize, range, etc.) are only updated inside the onChange callback. However, Virtualizer.setOptions() does not itself trigger notify(), and _willUpdate() only notifies when the scroll element changes (or via subsequent scroll/resize observers). This means option-only changes (e.g. count changes from a signal, which is a documented use case) can leave these signals stale until an unrelated scroll/resize happens. To keep the Angular signals consistent, update them once after applying options (or otherwise force a notify) within this effect run.

Suggested change

})

})

// Ensure adapter signals stay in sync even when only options change

virtualItems.set(instance.getVirtualItems())

totalSize.set(instance.getTotalSize())

isScrolling.set(instance.isScrolling)

range.set(instance.range)

scrollDirection.set(instance.scrollDirection)

scrollElement.set(instance.scrollElement)

scrollOffset.set(instance.scrollOffset)

scrollRect.set(instance.scrollRect)

Copilot · 2026-03-12T19:03:39Z

packages/angular-virtual/src/index.ts

+        case 'scrollOffset':
+          return scrollOffset
+        case 'scrollRect':
+          return scrollRect


Previously, the adapter wrapped several argument-taking Virtualizer methods (e.g. getOffsetForIndex, getVirtualItemForOffset, indexFromElement) so their results became reactive to virtualizer updates when used from signal-driven templates/computeds. With the new proxy, these methods fall through to Reflect.get and no longer read any Angular signal, so their return values won’t automatically update when the virtualizer state changes. If this reactivity was intentional (it was explicitly implemented in the removed proxy.ts), consider reintroducing a reactive wrapper for these methods or documenting the behavior change as it can break existing consumers.

Suggested change

return scrollRect

return scrollRect

case 'getOffsetForIndex':

case 'getVirtualItemForOffset':

case 'indexFromElement':

// Wrap argument-taking query methods so they read a signal and stay reactive

return (...args: unknown[]) => {

// Access a signal that updates on virtualizer changes to register dependency

virtualItems()

// Delegate to the underlying Virtualizer method

// eslint-disable-next-line @typescript-eslint/no-explicit-any

return (target as any)[prop](...args)

}

benjavicente

Hello 👋
I'm working on improving angular support from some of the libraries on the TanStack ecosystem. The Query adapter I'm working on has similar requirements and I can continue working in this issue if needed.

benjavicente · 2026-04-12T23:04:45Z

packages/angular-virtual/src/index.ts

-  function lazyInit() {
-    virtualizer ??= new Virtualizer(options())
-    return virtualizer
+  const instance = new Virtualizer<TScrollElement, TItemElement>(options())


You can't just call options() directly, since if that signal depends on Input signals, it will break with NG0952/NG0950. I wrote about it here for the Store adapter.

benjavicente · 2026-04-12T23:10:51Z

packages/angular-virtual/src/index.ts

+          scrollDirection.set(instance.scrollDirection)
+          scrollElement.set(instance.scrollElement)
+          scrollOffset.set(instance.scrollOffset)
+          scrollRect.set(instance.scrollRect)


I think you can keep the signal proxy pattern BUT if it works by lazy initializing the signal with a computed and by declaring what is a function vs a signal.

The Angular upgrade has a similar pattern here and here.

piecyk · 2026-04-13T16:48:27Z

Hi @Stallion8472 Thanks again for opening this PR, really appreciate it!

Since @benjavicente mentioned they’re working on improving Angular support across the TanStack ecosystem, I was wondering if you’d be comfortable with them picking this up and continuing the work here?

Stallion8472 added 2 commits January 5, 2026 13:57

fix: RuntimeError: NG0600: Writing to signals is not allowed in a com…

2935cc9

…puted or an effect by default by simplifying proxy

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fix(angular-virtual): RuntimeError: NG0600: Writing to signals is not allowed in a computed or an effect by default#1109

fix(angular-virtual): RuntimeError: NG0600: Writing to signals is not allowed in a computed or an effect by default#1109
Stallion8472 wants to merge 2 commits intoTanStack:mainfrom
Stallion8472:main

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-      })
+      })
+      // Ensure adapter signals stay in sync even when only options change
+      virtualItems.set(instance.getVirtualItems())
+      totalSize.set(instance.getTotalSize())
+      isScrolling.set(instance.isScrolling)
+      range.set(instance.range)
+      scrollDirection.set(instance.scrollDirection)
+      scrollElement.set(instance.scrollElement)
+      scrollOffset.set(instance.scrollOffset)
+      scrollRect.set(instance.scrollRect)

-          return scrollRect
+          return scrollRect
+        case 'getOffsetForIndex':
+        case 'getVirtualItemForOffset':
+        case 'indexFromElement':
+          // Wrap argument-taking query methods so they read a signal and stay reactive
+          return (...args: unknown[]) => {
+            // Access a signal that updates on virtualizer changes to register dependency
+            virtualItems()
+            // Delegate to the underlying Virtualizer method
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+            return (target as any)[prop](...args)
+          }

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