fix(uniqWith): match lodash comparator argument order in compat#1729
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The compat `uniqWith` passed the comparator straight to the non-compat implementation, which invokes it as `(kept, candidate)`. lodash documents and invokes the comparator as `(candidate, kept)`, so asymmetric comparators produced different results after migrating to es-toolkit/compat. Wrap the comparator to swap the arguments so the call order matches lodash.
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Pull request overview
Fixes es-toolkit/compat’s uniqWith to match lodash’s documented comparator argument order, ensuring asymmetric comparators behave identically when migrating from lodash.
Changes:
- Update compat
uniqWithto swap comparator arguments so calls become(candidate, kept)(lodash-compatible). - Add tests to assert comparator invocation order and verify behavior with an asymmetric “subset” comparator.
Reviewed changes
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| File | Description |
|---|---|
| src/compat/array/uniqWith.ts | Wraps the comparator to forward toolkit’s (kept, candidate) invocation as lodash’s (candidate, kept). |
| src/compat/array/uniqWith.spec.ts | Adds tests covering comparator argument order and an asymmetric comparator behavioral case. |
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raon0211
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May 22, 2026
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Thanks for catching ths!
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Summary
es-toolkit/compat'suniqWithinvoked the comparator with reversed argument order compared to lodash. lodash calls the comparator as(candidate, kept)(documented(arrVal, othVal)), but compat passed the comparator straight to the non-compat implementation, which calls it as(kept, candidate). Any asymmetric comparator silently produced different results after migrating from lodash.Changes
uniqWithso the toolkit's(kept, candidate)call is forwarded ascomparator(candidate, kept), matching lodash.(candidate, kept)order, plus a behavioral test for an asymmetric (subset) comparator.The non-compat
uniqWithkeeps its own documented(item1, item2)semantics and is unchanged.Test plan
yarn vitest run src/compat/array/uniqWith.spec.ts— 19 passed (new tests fail before the fix)yarn vitest run src/compat/array/— 1000 passeduniqWithunaffected; typecheck + lint cleanCloses #1728