TypeScript Union Types

Sometimes a variable legitimately needs to handle two different types of data. For example, a phone number might be a number (`5551234`) or a formatted text string (`"555-1234"`). Union types solve this problem.

1/* this uses a union type */
2function printID(id: number | string) {
3  console.log("The ID is: " + id);
4}
5
6printID(101);
7printID("A-101");