# `react-doctor/no-flush-sync`

Remove flushSync when a synchronous DOM commit is unnecessary; startTransition is only for explicitly non-urgent work, not a semantic replacement

- **Status:** Active
- **Category:** Performance
- **Assessment:** Evidence-required risk
- **Required evidence:** source code, runtime behavior, measurement
- **Default configuration:** Enabled
- **Default severity:** warn
- **Scope:** All supported frameworks
- **Active when:** always
- **Requirements:** react
- **Tags:** test-noise
- **Priority:** 34 (P3)
- **Source:** oxlint-plugin-react-doctor
- **Rule set:** oxlint-plugin-react-doctor 0.9.3 (prompt schema 2)

## Validation prompt

Confirm the detector match and collect the required evidence before deciding whether an edit is warranted.

Confirm an ImportDeclaration whose source is exactly "react-dom" with a named specifier flushSync, then inspect every call site because the rule reports only the import. flushSync is valid when browser or third-party imperative code must observe React's committed DOM before the next line runs, such as an onbeforeprint integration. It is not equivalent to startTransition: one forces an immediate commit while the other deliberately marks work as non-urgent.

## Evidence boundary

The diagnostic proves only that the detector's modeled source pattern matched. It does not prove runtime impact, product intent, rendered failure, or that one remediation is correct.

Establish the environment, explicit repository policy, relevant exceptions, and required rendered or runtime evidence before deciding the occurrence. This page’s Assessment and Required evidence fields define the review contract.

Default severity is registry metadata. Use the occurrence's JSON severity after repository configuration when ordering real findings.

Record one outcome:

- **Confirmed failure:** The required evidence establishes the violation.
- **Rejected:** A documented exception or false-positive predicate applies.
- **Needs evidence:** Named evidence can still be collected.
- **Unavailable:** Required evidence cannot be collected in this run.
- **Waived with evidence:** An authorized, scoped exception applies to an established failure.
- **Observation:** The review records an optional tradeoff without claiming a defect.

A waiver records its scope, authority, evidence, and review or expiry condition. It is not a pass or false positive.

## Fix prompt

Apply this candidate correction only after the required evidence confirms the risk.

When no synchronous DOM observation is required, remove the flushSync wrapper and use the ordinary state update. Use startTransition only when the update is independently known to be non-urgent and may be interrupted. Keep the narrowest flushSync boundary when an imperative integration requires the DOM to be committed before continuing, and test that integration. See https://react.dev/reference/react-dom/flushSync

## Repository-wide copy prompt

Use this only for a repository-wide pass after validating each occurrence. For one occurrence, use the occurrence-level guidance above.

````text
Fix every confirmed `react-doctor/no-flush-sync` diagnostic in the current repository.

Required change:
- When no synchronous DOM observation is required, remove the flushSync wrapper and use the ordinary state update. Use startTransition only when the update is independently known to be non-urgent and may be interrupted. Keep the narrowest flushSync boundary when an imperative integration requires the DOM to be committed before continuing, and test that integration. See https://react.dev/reference/react-dom/flushSync.

Validation before editing:
Confirm an ImportDeclaration whose source is exactly "react-dom" with a named specifier flushSync, then inspect every call site because the rule reports only the import. flushSync is valid when browser or third-party imperative code must observe React's committed DOM before the next line runs, such as an onbeforeprint integration. It is not equivalent to startTransition: one forces an immediate commit while the other deliberately marks work as non-urgent.

Constraints:
- Make the smallest change that fixes the root cause.
- Preserve behavior and interfaces unrelated to this diagnostic.
- Reuse existing project components, utilities, and conventions.
- Do not introduce render-phase side effects, render-phase state updates, or Hooks rule violations.
- Preserve resource ownership and cleanup. Do not move work into a hotter render or frame path.
- If syntax proves only a candidate cost, require a relevant trace, bundle report, payload measurement, or metric before editing.
- Without evidence, record Needs evidence. Compare the same scenario before and after; keep the change only when its target metric improves without regression.
- Adapt identifiers and framework details instead of copying blindly.
- Do not disable the rule or suppress matching code.

Assessment:
- Record detector evidence, applicability facts, assumptions, missing evidence, and the rule class for this occurrence.
- Return one outcome: Confirmed failure, Rejected, Needs evidence, Unavailable, Waived with evidence, or Observation.
- A waiver records the established failure, scope, authority, evidence, and review or expiry condition. It is not a pass or false positive.

Verification:
- Run focused tests for the changed behavior.
- Run React Doctor and confirm this diagnostic no longer appears from changed code.
- Run an unfiltered scan of the affected scope before claiming no cross-category regression.
- Report the files changed and any checks you could not run.
````