Did you know that Typescript(TS) has a data type called never? It messed with my head when I read about it.

Remember, Typescript does its best to narrow something down to its most specific type. You have a lot of control over this through Types and Interfaces. When you can't arrive at a type we can think of it as saying "this will never happen". Hence the never type. I'll show you two examples.

Firstly, a function can have a return type of never because of an exception within it. The function can't run to completion so it can never return a value.

// returns never because it fails to complete
function z(): never {
 throw Error()
}

Secondly, when you have exhausted the elements of a type all you have left is never. For example, this function expects one type as an input. It returns the same type. The switch statement it contains exhausts the legal values. The function parameter is type specific. Hence the default is never reached. It will be of type never

type Country  = 'england' | 'ireland'

function capitalize(x: Country): Country{
 switch(x){
 case 'england':
 case 'ireland':
 return x
 default:
 // x is of type `never`
 throw new Error(x)
  }
}

Hope you learnt something useful ❤️