react-doctor/js-combine-iterations
Fuse chained array iterations only when profiling identifies the chain as a hot path
- Status
- Active
- Category
- Performance
- Assessment
- Evidence-required risk
- Required evidence
- source code, runtime behavior, measurement
- Default configuration
- Enabled
- Default severity
- warn
Show technical metadata
- Scope
- All supported frameworks
- Active when
- always
- Tags
- test-noise
- Priority
- 26 (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.
The rule fires on chained calls whose methods are map, filter, forEach, or flatMap. Confirm a production profile shows the traversal or allocation is material and that callback order, side effects, holes, and exception timing can be preserved. For ordinary collections, the readable chain is often the better tradeoff.
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, repository policy, exceptions, and required rendered or runtime evidence before deciding the occurrence.
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 condition. It is not a pass or false positive.
Default severity is registry metadata. Use the occurrence’s JSON severity after repository configuration when ordering real findings.
Fix prompt
Apply this candidate correction only after the required evidence confirms the risk.
For a confirmed hot path, use a plain loop or reducer that preserves the original callback order, side effects, sparse-array behavior, and output semantics. Do not use flatMap as an allocation-free fix because returning empty or singleton arrays can allocate per item. Benchmark the real data before retaining the rewrite. See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flatMap
Repository-wide copy prompt
Use this repository-wide prompt only after validating each occurrence. For one occurrence, use the guidance above.
Show repository-wide prompt
Fix every confirmed react-doctor/js-combine-iterations diagnostic in the current repository.
Required change:
- For a confirmed hot path, use a plain loop or reducer that preserves the original callback order, side effects, sparse-array behavior, and output semantics. Do not use flatMap as an allocation-free fix because returning empty or singleton arrays can allocate per item. Benchmark the real data before retaining the rewrite. See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flatMap.
Validation before editing:
The rule fires on chained calls whose methods are map, filter, forEach, or flatMap. Confirm a production profile shows the traversal or allocation is material and that callback order, side effects, holes, and exception timing can be preserved. For ordinary collections, the readable chain is often the better tradeoff.
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.
- 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.