Disallows usage of void
type outside of generic or return types (no-invalid-void-type
)
Disallows usage of void
type outside of return types or generic type arguments.
If void
is used as return type, it shouldn’t be a part of intersection/union type with most other types.
Rationale
The void
type means “nothing” or that a function does not return any value,
in contrast with implicit undefined
type which means that a function returns a value undefined
.
So “nothing” cannot be mixed with any other types, other than never
, which accepts all types.
If you need this - use the undefined
type instead.
Rule Details
This rule aims to ensure that the void
type is only used in valid places.
Examples of code for this rule:
- ❌ Incorrect
- âś… Correct
type PossibleValues = string | number | void;
type MorePossibleValues = string | ((number & any) | (string | void));
function logSomething(thing: void) {}
function printArg<T = void>(arg: T) {}
logAndReturn<void>(undefined);
interface Interface {
lambda: () => void;
prop: void;
}
class MyClass {
private readonly propName: void;
}
type NoOp = () => void;
function noop(): void {}
let trulyUndefined = void 0;
async function promiseMeSomething(): Promise<void> {}
type stillVoid = void | never;
Options
interface Options {
allowInGenericTypeArguments?: boolean | string[];
allowAsThisParameter?: boolean;
}
const defaultOptions: Options = {
allowInGenericTypeArguments: true,
allowAsThisParameter: false,
};
allowInGenericTypeArguments
This option lets you control if 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 }
:
logAndReturn<void>(undefined);
let voidPromise: Promise<void> = new Promise<void>(() => {});
let voidMap: Map<string, void> = new Map<string, void>();
The following patterns are considered warnings with { allowInGenericTypeArguments: ['Ex.Mx.Tx'] }
:
logAndReturn<void>(undefined);
type NotAllowedVoid1 = Mx.Tx<void>;
type NotAllowedVoid2 = Tx<void>;
type NotAllowedVoid3 = Promise<void>;
The following patterns are not considered warnings with { allowInGenericTypeArguments: ['Ex.Mx.Tx'] }
:
type AllowedVoid = Ex.Mx.Tx<void>;
type AllowedVoidUnion = void | Ex.Mx.Tx<void>;
allowAsThisParameter
This option allows specifying a this
parameter of a function to be void
when set to true
.
This pattern can be useful to explicitly label function types that do not use a this
argument. See the TypeScript docs for more information.
This option is false
by default.
The following patterns are considered warnings with { allowAsThisParameter: false }
but valid with { allowAsThisParameter: true }
:
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.
Related To
- TSLint: invalid-void
Attributes
- âś… Recommended
- 🔧 Fixable
- đź’ Requires type information