function buildName(firstName: string, lastName = "Smith") { return firstName + " " + lastName; } let result1 = buildName("Bob"); //works correctly now, returns "Bob Smith" let result2 = buildName("Bob", undefined); //still works, also returns "Bob Smith" let result3 = buildName("Bob", "Adams", "Sr.");//error, too many parameters let result4 = buildName("Bob", "Adams"); //ah, just right