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Unions

As someone that writes a lot of Go, union types are the thing I'm most jealous of in TypeScript. I love them.

Union types use the pipe symbol (|) and allow you to specify that a value can be one of several types.

// userId is a string OR a number
let userId: string | number;
userId = "user_42";
userId = 42;

Unions are perfect for when a value could be one of several types. One really cool thing about TypeScript is that conditional checks actually change the type of a variable. This is called "type narrowing". Take a look:

function safeSquare(val: string | number): number {
  if (typeof val === "string") {
    val = parseInt(val, 10);
  }
  // now val is only a number
  return val * val;
}

let result = safeSquare("5");
console.log(result);
// 25

result = safeSquare(5);
console.log(result);
// 25

Assignment

At Support.ai, we're upgrading our ticket processing system to handle different types of ticket identifiers. Our clients use both numeric IDs (like 42) and project codes (like "SUPPORT-123"), and our system needs to process both formats uniformly.

Update the getTicketInfo function to only accept an id that's a string or a number.
If the id is a string, parse the number part out of it.
Return the string Processing ticket: ID, where ID is either the ID number, or the parsed number from the project code.

Tips

The .split() method on the - delimiter will be useful for parsing the number part out of a project code.