typescript how to define a funxtion as a type code example

Example 1: typescript default parameter

function sayName({ first, last = 'Smith' }: {first: string; last?: string }): void {
  const name = first + ' ' + last;
  console.log(name);
}

sayName({ first: 'Bob' });

Example 2: typescript annotate return type

function add(x: number, y: number): number {
  return x + y;
}