Optional parameters let you model inputs that may or may not be provided. In TypeScript, an optional parameter x?: T is seen as T | undefined at the type level.
You’ll write a greet function that optionally accepts a title, like 'Dr.' or 'Ms.', and formats the greeting accordingly.
greet(name: string, title?: string): string.title is provided, return 'Hello, ' + title + ' ' + name.'Hello, ' + name.greet('Alex') // 'Hello, Alex'
greet('River', 'Dr.') // 'Hello, Dr. River'