---
description: 'Disallow `void` type outside of generic or return types.'
---
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> 🛑 This file is source code, not the primary documentation location! 🛑
>
> See **https://typescript-eslint.io/rules/no-invalid-void-type** for documentation.
`void` in TypeScript refers to a function return that is meant to be ignored.
Attempting to use a `void` type outside of a return type or generic type argument is often a sign of programmer error.
`void` can also be misleading for other developers even if used correctly.
> The `void` type means cannot be mixed with any other types, other than `never`, which accepts all types.
> If you think you need this then you probably want the `undefined` type instead.
## Examples
```ts
type PossibleValues = string | number | void;
type MorePossibleValues = string | ((number & any) | (string | void));
function logSomething(thing: void) {}
function printArg(arg: T) {}
logAndReturn(undefined);
interface Interface {
lambda: () => void;
prop: void;
}
class MyClass {
private readonly propName: void;
}
```
```ts
type NoOp = () => void;
function noop(): void {}
let trulyUndefined = void 0;
async function promiseMeSomething(): Promise {}
type stillVoid = void | never;
```
## Options
### `allowInGenericTypeArguments`
Whether `void` can be used as a valid value for generic type parameters.
Alternatively, you can provide an array of strings which whitelist which types may accept `void` as a generic type parameter.
Any types considered valid by this option will be considered valid as part of a union type with `void`.
This option is `true` by default.
The following patterns are considered warnings with `{ allowInGenericTypeArguments: false }`:
```ts option='{ "allowInGenericTypeArguments": false }' showPlaygroundButton
logAndReturn(undefined);
let voidPromise: Promise = new Promise(() => {});
let voidMap: Map = new Map();
```
The following patterns are considered warnings with `{ allowInGenericTypeArguments: ['Ex.Mx.Tx'] }`:
```ts option='{ "allowInGenericTypeArguments": ["Ex.Mx.Tx"] }' showPlaygroundButton
logAndReturn(undefined);
type NotAllowedVoid1 = Mx.Tx;
type NotAllowedVoid2 = Tx;
type NotAllowedVoid3 = Promise;
```
The following patterns are not considered warnings with `{ allowInGenericTypeArguments: ['Ex.Mx.Tx'] }`:
```ts option='{ "allowInGenericTypeArguments": ["Ex.Mx.Tx"] }' showPlaygroundButton
type AllowedVoid = Ex.Mx.Tx;
type AllowedVoidUnion = void | Ex.Mx.Tx;
```
### `allowAsThisParameter`
Whether a `this` parameter of a function may be `void`.
This pattern can be useful to explicitly label function types that do not use a `this` argument. [See the TypeScript docs for more information](https://www.typescriptlang.org/docs/handbook/functions.html#this-parameters-in-callbacks).
This option is `false` by default.
The following patterns are considered warnings with `{ allowAsThisParameter: false }` but valid with `{ allowAsThisParameter: true }`:
```ts option='{ "allowAsThisParameter": false }' showPlaygroundButton
function doThing(this: void) {}
class Example {
static helper(this: void) {}
callback(this: void) {}
}
```
## When Not To Use It
If you don't care about if `void` is used with other types, or in invalid places, then you don't need this rule.