array-callback-return

Methods like map and filter use the callback's return value. If the callback forgets return, they get undefined, so map fills the array with undefined and filter drops every item. A callback that only returns a value on some paths is reported too.

The rule checks a function passed directly to every, filter, find, findIndex, findLast, findLastIndex, flatMap, map, reduce, reduceRight, some, sort, toSorted, Array.from or Array.fromAsync.

Configure

Off by default. To turn it on:

[lint.rules]
"array-callback-return" = "error" # or "warn"

Every option, set to its default:

[lint.rules]
"array-callback-return" = ["error", {
  allowImplicit = false,
  checkForEach = false,
  allowVoid = false,
}]

Examples

Reported:

const names = users.map(user => {
  user.name.trim();
});

const adults = users.filter(user => {
  if (user.age >= 18) {
    return true;
  }
});

Not reported:

const names = users.map(user => {
  return user.name.trim();
});

const adults = users.filter(user => user.age >= 18);

Options

Option	Default	What it does
allowImplicit	false	Allow return; without a value as a way to return undefined.
checkForEach	false	Also check forEach, but the other way around. A callback that returns a value is reported, because forEach ignores it.
allowVoid	false	With checkForEach, allow a returned value that starts with void.

const first = users.find(user => {
  if (!user.active) {
    return;
  }
  return user.admin;
});

users.forEach(user => save(user));

users.forEach(user => {
  save(user);
});

users.forEach(user => void save(user));