Unions allow variables to hold one of several specified types.

type ColorValue = number | "red" | "green" | "blue";
type WindowState = "open" | "closed" | "minimized";

function wrapInArray(obj: string | string[]): string[] {
  // If obj is a string, wrap it in an array; else, return the array as-is.
  return typeof obj === "string" ? [obj] : obj;
}

// Example usage:
console.log(wrapInArray("hello"));        // Output: ["hello"]
console.log(wrapInArray(["hello", "hi"]));  // Output: ["hello", "hi"]