When TypeScript's void type is used in combination with other types through intersection, the outcomes vary.
type A = void & {} // A becomes void & {}
type B = void & '1' // B becomes never
type C = void & 1 // C becomes never
type D = void & string // D becomes never
type E = void & String // E becomes void & String
type A = void & {}
type E = void & String
Shouldn't they all be never types, though?
{} and String both fall under object types, while string and '1' are considered primitive types. Intersection of void with object types is possible due to the addition of properties:
type A = { foo: number } & { bar: string } // { foo: number, bar: string }
In contrast, intersection of primitive types involves narrowing down the set of values:
type B = string & 'abc' // 'abc'
You can extend primitive types by intersecting them with object types:
type C = string & { foo: number }
declare const c: C
c.foo // number
However, intersecting two different primitive types results in never:
type D = string & number // never
type E = 1 & 2 // never
It's important to note that void is a primitive type.
Therefore, void & { foo: number } implies that the primitive void will possess the property foo.
On the other hand, void & string leads to a result of never since they are distinct primitive types.
Yet, void & String equates to void with the characteristics of String because String is an object type (generated by new String()).
In practice, assigning anything other than undefined to void is not feasible, as undefined cannot possess properties. Thus, I would argue that having void & Type serve no practical purpose in your codebase. If you believe it is necessary, consider refactoring your code to eliminate this need.
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