打字稿：定义一个不能容纳任何东西的类型

Question

I'm interested (for the purpose of validation) in such a type, that variables of this type cannot have any value assigned to them. There is type void , but value of this type can contain the value undefined , so it's not exactly what I'm asking about.

It seems that I'm able to reproduce this behaviour used the intersection of incompatible types:

type nothing = true & false;
const nothingTrue: nothing = true; // error, true not assignable to false
const nothingFalse: nothing = false; // error, false not assignable to true
const nothingUndefined: nothing = undefined; // error, undefined not assignable to true

But this looks more like a hack. Maybe there is something more clear? Or is this the right way?

Answer 1

The type you are looking for is the never type. From the docs :

The never type is a subtype of, and assignable to, every type; however, no type is a subtype of, or assignable to, never (except never itself). Even any isn't assignable to never.