Backend function trigger throws internal runtime error

💬 App Building
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Backend function trigger throws internal runtime error (void 0) is not a function — stack trace points into Retool's own bundle, not app code

RETOOL RUNTIME ERROR
RETOOL RUNTIME ERROR1046×148 14.6 KB

What's happening:
Calling .trigger(...).result on a generated backend-function hook (via useBackendFunctions.ts) intermittently throws TypeError: (void 0) is not a function. The stack trace resolves into Retool's own compiled runtime bundle (assets/index.js), not into any app code — confirmed by wrapping the call in a local try/catch and logging the full error/stack, rather than relying on the generic error banner.

  1. Environment: Sandbox app (agent-sandbox.retool.com), production-mode published build.

    Reproduction pattern:

    • Backend function: /backend/estimateCenter/createEstimate.ts

    • Error fires on save/submit from the frontend page calling this function's hook

    • Same error appears in both [hookName].error (Retool's built-in error state) and in a manually-caught try/catch around the same call — identical text and stack in both, confirming it's thrown before reaching app code

    • Persisted across multiple different rewrites of the backend function's internal logic (different implementations, same trigger call) — ruling out an app-code cause

    • Reproduced in a fresh incognito window — ruling out client-side cache

    Other reliability issues observed in the same session, possibly related:

    1. Auto-generated hooks file wiped entirely (useBackendFunctions.ts — all exports gone, not just ones tied to edited files) after saving unrelated backend files, and at least once after Publish with zero code changes. Recovered each time by resaving files individually until it regenerated.

    2. "This run involved a previous version of this function" shown in a function's run-history panel, despite the file being freshly saved and republished.

    3. Cloudflare 502 Bad Gateway on a backend function call that ran ~15–20+ seconds — confirmed via direct database check that the underlying work completed successfully server-side even though the response was lost.

    Attaching: screenshot of the error banner + the caught error with stack trace (index.js:126255:16).

2

Summary

On the new app builder (Cloud), calling .trigger(...).result on a generated backend-function hook (useBackendFunctions.ts) intermittently throws TypeError: (void 0) is not a function with a stack trace resolving into Retool's own compiled bundle, alongside related reliability issues — the generated hooks file being wiped after saving/publishing, stale 'previous version of this function' run history, and a Cloudflare 502 on a long-running backend function call that actually succeeded server-side.

AI Response

This behavior lines up with recently reported reliability issues in the new app builder's backend functions rather than app code. Retool published an incident on July 14, 2026 in which apps built in the new AI app builder showed an empty Data tab ("This app does not contain any functions") and could not publish because backend functions were flagged as unapproved or not visible — matching the symptom of the generated hooks file being wiped after save/publish; that incident is marked resolved. The pattern of regenerated code stranding or losing uncommitted edits in the new app builder is also independently corroborated in the community. For the long-running call, a Cloudflare 502 after 15–20+ seconds while the work completes server-side is consistent with a gateway timeout on the response rather than a failure of the function itself, so guarding against duplicate side effects and re-checking state after such calls is prudent. Note that the specific (void 0) is not a function runtime error thrown from Retool's own bundle does not have a directly matching public report or documented fix, so that exact signature remains unconfirmed.

Sources

:bookmark: https://status.retool.com
Retool's July 14, 2026 (resolved) incident — new app builder apps showing an empty Data tab and unable to publish because backend functions were unapproved/not visible — directly corroborates the disappearing/wiped generated functions symptom.
:bookmark: On New App Builder: Builder thread strands uncommitted edits — can't publish
A new app builder report of regenerated builder threads stranding uncommitted edits and blocking publish, corroborating the lost/regenerated backend function code reliability issue.

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