react-doctor/js-combine-iterations
Combine `.map().filter()` (or similar chains) into a single pass with `.reduce()` or a `for...of` loop to avoid iterating the array twice
- Category: Performance
- Severity: warn
- Source:
oxlint-plugin-react-doctor - Framework: global
- Enabled when: always
Validation prompt
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The rule fires on chained calls where both methods are in {map, filter, forEach, flatMap} — e.g. arr.map(fn).filter(pred) or arr.filter(pred).map(fn). The exact arr.map(fn).filter(Boolean) and arr.map(fn).filter(x => x) shapes are intentionally skipped (covered by js-flatmap-filter). False positive when the intermediate array is genuinely used elsewhere, or N is tiny enough that the extra pass is negligible.
Fix prompt
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Collapse into one pass with arr.flatMap(item => keep(item) ? [transform(item)] : []), arr.reduce((acc, item) => ..., []), or a plain for...of loop pushing into one output array. Avoids both the intermediate allocation and the second full traversal. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flatMap