Pro tip: Pass an object as function params and use destructuring

interface GreetingParams {
  name?: string; // keep this for backward compatbility
  firstName?: string; // replaces name
  lastName?: string;
  lastNameFirst?: boolean;
}

function greet({
  name,
  firstName = name, // if firstName not provided, use name as firstName
  lastName,
  lastNameFirst = false,
}: GreetingParams) {
  if (!lastName) {
    return `Hello, ${firstName}`;
  }
  return `Hello ${lastNameFirst ? lastName + " " + firstName : firstName + " " + lastName}`;
}

// Backward compatible with old signature
greet({ name: "John" });
// New signature with first name only
greet({ firstName: "John" });
// New signature with first name and last name
greet({ firstName: "John", lastName: "Doe" });
// New signature with first name and last name, last name first
greet({ firstName: "John", lastName: "Doe", lastNameFirst: true });