Lesson 11 — Optional params

Optional parameters

Adding ? after a parameter name (msg?: string) makes it optional: callers may leave it out, and then its value is undefined. Inside the function you give it a fallback — with ?? — or you write a default value (msg: string = "Hi") instead, which makes it optional automatically.

function tag(text: string, color?: string) {
  return text + " (" + (color ?? "grey") + ")";
}

Why it matters: optional inputs keep calls short for the common case without losing type checks.