---
url: /docs/guide/usage/linter/rules/typescript/promise-function-async.md
---

### What it does

This rule requires any function or method that returns a Promise to be marked as async.

### Why is this bad?

Functions that return Promises should typically be marked as `async` to make their asynchronous nature clear and to enable the use of `await` within them. This makes the code more readable and helps prevent common mistakes with Promise handling.

### Examples

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

```ts
// Function returning Promise without async
function fetchData(): Promise<string> {
  return fetch("/api/data").then((res) => res.text());
}

// Method returning Promise without async
class DataService {
  getData(): Promise<any> {
    return fetch("/api/data").then((res) => res.json());
  }
}

// Arrow function returning Promise without async
const processData = (): Promise<void> => {
  return Promise.resolve();
};
```

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

```ts
// Async function
async function fetchData(): Promise<string> {
  const response = await fetch("/api/data");
  return response.text();
}

// Async method
class DataService {
  async getData(): Promise<any> {
    const response = await fetch("/api/data");
    return response.json();
  }
}

// Async arrow function
const processData = async (): Promise<void> => {
  await someAsyncOperation();
};

// Functions that don't return Promise are fine
function syncFunction(): string {
  return "hello";
}

// Functions returning Promise-like but not actual Promise
function createThenable(): { then: Function } {
  return { then: () => {} };
}
```

## Configuration

This rule accepts a configuration object with the following properties:

### allowAny

type: `boolean`

default: `true`

Whether to allow functions returning `any` type without requiring `async`.

### allowedPromiseNames

type: `string[]`

default: `[]`

A list of Promise type names that are allowed without requiring `async`.
Example: `["SpecialPromise"]` to allow functions returning `SpecialPromise` without `async`.

### checkArrowFunctions

type: `boolean`

default: `true`

Whether to check arrow functions for missing `async` keyword.

### checkFunctionDeclarations

type: `boolean`

default: `true`

Whether to check function declarations for missing `async` keyword.

### checkFunctionExpressions

type: `boolean`

default: `true`

Whether to check function expressions for missing `async` keyword.

### checkMethodDeclarations

type: `boolean`

default: `true`

Whether to check method declarations for missing `async` keyword.

## How to use

## Version

This rule was added in v1.12.0.

## References