@studnicky/v8/chained-array-iteration

Disallows two or more built-in every, filter, find, flatMap, forEach, map, reduce, or some passes along one Array or ReadonlyArray call chain, including when non-iterating calls appear between them. It also detects an adjacent const temporary that holds one such call and has exactly one use as the receiver of the next. The rule resolves signatures, so same-named methods on unrelated fluent APIs are not reported.

For a 5,000,000-element array in Node v24, map(...).filter(...) takes 54.09 ms while a single reduce takes 26.76 ms: 2.02× slower, or 102% more time. Combine transformation and selection into one pass where the chain represents repeated traversal.

Fixable: No · Options: No · Suggested severity: error

✗ Incorrect

const names = users.filter((user) => user.active).map((user) => user.name);

const activeUsers = users.filter((user) => user.active);
const names = activeUsers.map((user) => user.name);

✓ Correct

const names = users.reduce<string[]>((result, user) => {
  if (user.active) {
    result.push(user.name);
  }
  return result;
}, []);

const visible = users.reduce<typeof users>((result, user) => {
  if (user.visible) {
    result.push(user);
  }
  return result;
}, []);