function myFunction(a: number, b?:number): number {
             if (typeof b !== 'undefined'){
                     return a+b+5;
                  } else {
                          return a+5;
                  }
          }

console.log(myFunction(1,2));
console.log(myFunction(1));
console.log(myFunction(3,5));
console.log(myFunction(3));
8
6
13
8