# n/callback-return

> Require a `return` with every call to a callback

Calling a callback doesn't end the function. Without a `return`, the code after the call keeps running, and the callback often gets called a second time.

The rule looks at calls to `callback`, `cb` and `next` inside functions. A call is fine if you return it, if a `return` comes right after it, or if it's the last statement in the function.

{/* Generated by src/codegen/lint-rule-docs.ts. Do not edit this section. */}

## Configure

Off by default. To turn it on:

```toml bunfig.toml
[lint.rules]
"n/callback-return" = "error" # or "warn"
```

{/* End of the generated section. */}

## Examples

Reported:

{/* bad */}
```js
function loadUser(id, callback) {
  if (!id) {
    callback(new Error("missing id"));
  }
  db.find(id, callback);
}
```

Not reported:

{/* good */}
```js
function loadUser(id, callback) {
  if (!id) {
    return callback(new Error("missing id"));
  }
  db.find(id, callback);
}

function saveUser(user, callback) {
  if (!user.id) {
    callback(new Error("missing id"));
    return;
  }
  callback(null, db.save(user));
}
```

The rule doesn't follow control flow. A call at the end of an `if` block is reported even if nothing runs after it:

{/* bad */}
```js
function loadUser(id, callback) {
  if (!id) {
    callback(new Error("missing id"));
  } else {
    db.find(id, callback);
  }
}
```

## Options

The option is the list of names that count as callbacks. It replaces the default, `["callback", "cb", "next"]`. A name can be a path such as `"res.send"`.

```toml bunfig.toml
[lint.rules]
"n/callback-return" = ["error", ["done", "res.send"]]
```

{/* bad {"options": [["done", "res.send"]]} */}
```js
function show(req, res) {
  if (!req.user) {
    res.send(401);
  }
  res.render("profile");
}
```

{/* good {"options": [["done", "res.send"]]} */}
```js
function show(req, res, next) {
  if (!req.user) {
    next();
  }
  res.render("profile");
}
```

## When not to use it

The rule goes by names. It reports a function named `next` that isn't a callback, and misses a callback with another name. Code that uses promises and `async` functions doesn't need it.