Typescript: ReturnType of overloaded function

Question

The type given by ReturnType seems to depend on the order the overload signatures are written

function applyChanges1(input: string): number
func         


        

Answer 1

This is a known limitation. The TypeScript team's recommendation is to include a "most general" overload signature as your last overload signature, e.g.:

function applyChanges1(input: string): number
function applyChanges1(input: number): string
function applyChanges1(input: number | string): number | string
function applyChanges1(input: number | string): number | string {
  return typeof input === "number" ? input.toString() : input.length
}

Titian Cernicova-Dragomir has a nicer alternate solution in his answer.