react-doctor/jotai-derived-atom-returns-fresh-object

Split the derivation into per-field primitive derived atoms, or wrap with selectAtom(source, fn, shallow) from jotai/utils when a wrapper object is required.

  • Category: State & Effects
  • Severity: warn
  • Source: oxlint-plugin-react-doctor
  • Framework: global
  • Enabled when: always

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Fires only on a CallExpression to jotai's imported atom (verified via the import binding, local-name aliasing allowed) whose FIRST argument is a function with EXACTLY one Identifier parameter (the get param), where that body both (a) references the get parameter as a call somewhere not nested in an inner function, and (b) returns a fresh structure: a bare ObjectExpression/ArrayExpression literal (including spread { ...get(x) }), or a method chain whose OUTERMOST call is an array-producing instance method (filter, map, flatMap, slice, concat, flat, toSorted, toReversed, toSpliced, with, sort, reverse — note sort/reverse mutate-and-return their receiver rather than allocate) or a static Object.{keys,values,entries,fromEntries,assign,create} / Array.{from,of} call. For block bodies every reachable top-level return must be fresh. The detector never inspects the atom() call's second argument. False positives a reviewer would suppress: a reader function that takes more than one parameter (e.g. (get, set) => ...) or zero params, skipped because only single-Identifier-param readers are inspected — this is why the read-write fixture is also quiet, since its reader (get) => get(baseAtom) additionally returns a reference-stable get(x) member value; chains whose outermost terminator returns a primitive or stable value (.filter(...).reduce(...), .find(), .some(), .includes(), .join(), .items.length); a plain get(x).user member access (reference-stable); a constant atom whose body never calls get; an atom imported from a non-jotai module; and block bodies that mix one fresh return with one reference-stable return.

Fix prompt

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jotai propagates derived values with Object.is and has no shallow compare on a plain atom, so a fresh object/array every read re-renders every consumer on every upstream notify even when fields are unchanged. Either split the wrapper into one primitive derived atom per field (e.g. const countAtom = atom((get) => get(cartAtom).items.length) and a separate totalAtom), each of which dedupes via Object.is, or if a single wrapper object is genuinely required wrap it with selectAtom(sourceAtom, (s) => ({ ... }), shallow) from jotai/utils (importing shallow) so equal shapes are deduped. For array chains, memoize the source or move the allocation to the consumer.