What is the best way to type the parameters of a function?

Question

typescript

How best to type the parameters of a function, for example, through an interface or type, an example is needed. Yes, I understand that in the case with undefinedit will be NaN, but I'm interested in the typing of function parameters so that there are no such clutter asa: number | undefined, b: number | undefined

function sum (a: number | undefined, b: number | undefined) {
  return a + b
}

sum(1,3)

Answer 1

If we omit the fact that the parameters of the addition function must be defined as mandatory, then the specific type undefinedcan be replaced with an optional modifier ?.
function а (a?: number, b?: number) {}
Otherwise, the parameters of the declaration function cannot be described. Another thing is a functional expression that can be described using a type.
For alias
type Sum = (a?: number, b?: number) => number;
For interface

interface ISum { (a?: number, b?: number): number; }

and use
const sum: Sum = (a, b) => a + b;