In simple english can anyone explain why and when to use the never type?

I've been struggling to understand when to use the never type, so can anyone explain and give some scenarios when to use the never type? I've read about it being use in endless loops and stuff but, still don't quite get it. can anyone explain when to use the never type and in what scenario?

I couldn't wrap my head around the concept, I've tried reading blogs and articles, I just can see where should i use it.

You may have more luck if you give up trying to find a reason for never and simply exploit the rules of the game. never is used all over the place for different reasons, it is a multi-purpose tool. You will find use cases as you go when doing type-level programming.

Properties:

• never extends everything
• only never and any extend never
• never & T is never
• never | T is T

Some quirks:

• any extends never ? X : Y is X | Y
• [any] extends [never] ? X : Y is Y
• T extends U ? X : Y is never if T is never
• [T] extends [U] ? X : Y is what you expect depending on U

An example of a way to exploit these properties: knowing that never | T is T, if you are constructing a union and you want to filter out some of its members, you will intentionally produce never values expecting that they will be swallowed later.

For user-facing types, a rule of thumb is simply to avoid using never and any as values, but to use them as constraints or parameter types. never then becomes a cheap way to forbid a value. For example:

• if you want to forbid objects containing the key foo: write { foo?: never } as a constraint or parameter type.
• if you want to reject certain inputs but you can't think of a type definition: write a utility type that returns never when the input doesn't meet your requirements: <A extends Check<A>>(a: A) => whatever (where Check<T> may return never)