---
url: /docs/guide/usage/linter/rules/promise/always-return.md
---

### What it does

Require returning inside each `then()` to create readable and reusable Promise chains.
We also allow someone to throw inside a `then()` which is essentially the same as return `Promise.reject()`.

### Why is this bad?

Broken Promise Chain.
Inside the first `then()` callback, a function is called but not returned.
This causes the next `then()` in the chain to execute immediately without waiting for the called function to complete.

### Examples

Examples of **incorrect** code for this rule:

```javascript
myPromise.then(function (val) {});
myPromise.then(() => {
  doSomething();
});
myPromise.then((b) => {
  if (b) {
    return "yes";
  } else {
    forgotToReturn();
  }
});
```

Examples of **correct** code for this rule:

```javascript
myPromise.then((val) => val * 2);
myPromise.then(function (val) {
  return val * 2;
});
myPromise.then(doSomething); // could be either
myPromise.then((b) => {
  if (b) {
    return "yes";
  } else {
    return "no";
  }
});
```

## Configuration

This rule accepts a configuration object with the following properties:

### ignoreAssignmentVariable

type: `string[]`

default: `["globalThis"]`

You can pass an `{ ignoreAssignmentVariable: [] }` as an option to this rule
with a list of variable names so that the last `then()` callback in a promise
chain does not warn if it does an assignment to a global variable. Default is
`["globalThis"]`.

```javascript
/* promise/always-return: ["error", { ignoreAssignmentVariable: ["globalThis"] }] */

// OK
promise.then((x) => {
  globalThis = x;
});

promise.then((x) => {
  globalThis.x = x;
});

// OK
promise.then((x) => {
  globalThis.x.y = x;
});

// NG
promise.then((x) => {
  anyOtherVariable = x;
});

// NG
promise.then((x) => {
  anyOtherVariable.x = x;
});

// NG
promise.then((x) => {
  x();
});
```

### ignoreLastCallback

type: `boolean`

default: `false`

You can pass an `{ ignoreLastCallback: true }` as an option to this rule so that
the last `then()` callback in a promise chain does not warn if it does not have
a `return`. Default is `false`.

```javascript
// OK
promise.then((x) => {
  console.log(x);
});
// OK
void promise.then((x) => {
  console.log(x);
});
// OK
await promise.then((x) => {
  console.log(x);
});

promise
  // NG
  .then((x) => {
    console.log(x);
  })
  // OK
  .then((x) => {
    console.log(x);
  });

// NG
const v = promise.then((x) => {
  console.log(x);
});
// NG
const v = await promise.then((x) => {
  console.log(x);
});
function foo() {
  // NG
  return promise.then((x) => {
    console.log(x);
  });
}
```

## How to use

## Version

This rule was added in v1.13.0.

## References