---
description: 'Disallow Promises in places not designed to handle them.'
---

import Tabs from '@theme/Tabs';
import TabItem from '@theme/TabItem';

> 🛑 This file is source code, not the primary documentation location! 🛑
>
> See **https://typescript-eslint.io/rules/no-misused-promises** for documentation.

This rule forbids providing Promises to logical locations such as if statements in places where the TypeScript compiler allows them but they are not handled properly.
These situations can often arise due to a missing `await` keyword or just a misunderstanding of the way async
functions are handled/awaited.

:::tip
`no-misused-promises` only detects code that provides Promises to incorrect _logical_ locations.
See [`no-floating-promises`](./no-floating-promises.mdx) for detecting unhandled Promise _statements_.
:::

## Options

### `checksConditionals`

If you don't want to check conditionals, you can configure the rule with `"checksConditionals": false`:

```json
{
  "@typescript-eslint/no-misused-promises": [
    "error",
    {
      "checksConditionals": false
    }
  ]
}
```

Doing so prevents the rule from looking at code like `if (somePromise)`.

Examples of code for this rule with `checksConditionals: true`:

## Examples

<Tabs>
<TabItem value="❌ Incorrect">

```ts option='{ "checksConditionals": true }'
const promise = Promise.resolve('value');

if (promise) {
  // Do something
}

const val = promise ? 123 : 456;

while (promise) {
  // Do something
}
```

</TabItem>
<TabItem value="✅ Correct">

```ts option='{ "checksConditionals": true }'
const promise = Promise.resolve('value');

// Always `await` the Promise in a conditional
if (await promise) {
  // Do something
}

const val = (await promise) ? 123 : 456;

while (await promise) {
  // Do something
}
```

</TabItem>
</Tabs>

### `checksVoidReturn`

Likewise, if you don't want to check functions that return promises where a void return is
expected, your configuration will look like this:

```json
{
  "@typescript-eslint/no-misused-promises": [
    "error",
    {
      "checksVoidReturn": false
    }
  ]
}
```

You can disable selective parts of the `checksVoidReturn` option by providing an object that disables specific checks.
The following options are supported:

- `arguments`: Disables checking an asynchronous function passed as argument where the parameter type expects a function that returns `void`
- `attributes`: Disables checking an asynchronous function passed as a JSX attribute expected to be a function that returns `void`
- `properties`: Disables checking an asynchronous function passed as an object property expected to be a function that returns `void`
- `returns`: Disables checking an asynchronous function returned in a function whose return type is a function that returns `void`
- `variables`: Disables checking an asynchronous function used as a variable whose return type is a function that returns `void`

For example, if you don't mind that passing a `() => Promise<void>` to a `() => void` parameter or JSX attribute can lead to a floating unhandled Promise:

```json
{
  "@typescript-eslint/no-misused-promises": [
    "error",
    {
      "checksVoidReturn": {
        "arguments": false,
        "attributes": false
      }
    }
  ]
}
```

Examples of code for this rule with `checksVoidReturn: true`:

<Tabs>
<TabItem value="❌ Incorrect">

```ts option='{ "checksVoidReturn": true }'
[1, 2, 3].forEach(async value => {
  await doSomething(value);
});

new Promise(async (resolve, reject) => {
  await doSomething();
  resolve();
});

const eventEmitter = new EventEmitter();
eventEmitter.on('some-event', async () => {
  synchronousCall();
  await doSomething();
  otherSynchronousCall();
});
```

</TabItem>
<TabItem value="✅ Correct">

```ts option='{ "checksVoidReturn": true }'
// for-of puts `await` in outer context
for (const value of [1, 2, 3]) {
  await doSomething(value);
}

// If outer context is not `async`, handle error explicitly
Promise.all(
  [1, 2, 3].map(async value => {
    await doSomething(value);
  }),
).catch(handleError);

// Use an async IIFE wrapper
new Promise((resolve, reject) => {
  // combine with `void` keyword to tell `no-floating-promises` rule to ignore unhandled rejection
  void (async () => {
    await doSomething();
    resolve();
  })();
});

// Name the async wrapper to call it later
const eventEmitter = new EventEmitter();
eventEmitter.on('some-event', () => {
  const handler = async () => {
    await doSomething();
    otherSynchronousCall();
  };

  try {
    synchronousCall();
  } catch (err) {
    handleSpecificError(err);
  }

  handler().catch(handleError);
});
```

</TabItem>
</Tabs>

### `checksSpreads`

If you don't want to check object spreads, you can add this configuration:

```json
{
  "@typescript-eslint/no-misused-promises": [
    "error",
    {
      "checksSpreads": false
    }
  ]
}
```

Examples of code for this rule with `checksSpreads: true`:

<Tabs>
<TabItem value="❌ Incorrect">

```ts option='{ "checksSpreads": true }'
const getData = () => someAsyncOperation({ myArg: 'foo' });

return { foo: 42, ...getData() };

const getData2 = async () => {
  await someAsyncOperation({ myArg: 'foo' });
};

return { foo: 42, ...getData2() };
```

</TabItem>
<TabItem value="✅ Correct">

```ts option='{ "checksSpreads": true }'
const getData = () => someAsyncOperation({ myArg: 'foo' });

return { foo: 42, ...(await getData()) };

const getData2 = async () => {
  await someAsyncOperation({ myArg: 'foo' });
};

return { foo: 42, ...(await getData2()) };
```

</TabItem>
</Tabs>

## When Not To Use It

This rule can be difficult to enable on large existing projects that set up many misused Promises.
Alternately, if you're not worried about crashes from floating or misused Promises -such as if you have global unhandled Promise handlers registered- then in some cases it may be safe to not use this rule.
You might consider using [ESLint disable comments](https://eslint.org/docs/latest/use/configure/rules#using-configuration-comments-1) for those specific situations instead of completely disabling this rule.

## Further Reading

- [TypeScript void function assignability](https://github.com/Microsoft/TypeScript/wiki/FAQ#why-are-functions-returning-non-void-assignable-to-function-returning-void)

## Related To

- [`no-floating-promises`](./no-floating-promises.mdx)
