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:

bunfig.toml

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

Every option, set to its default:

bunfig.toml

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

Examples#

example.js1 problem

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

example.js1 problem

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

example.jsNo problems

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`.

example.jswith { "allowImplicit": true }No problems

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

example.jswith { "checkForEach": true }1 problem

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

example.jswith { "checkForEach": true }No problems

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

example.jswith { "checkForEach": true, "allowVoid": true }No problems

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