Literal types

In addition to the general types string and
number, we can refer to specific strings and
numbers in type positions.

let changingString = "Hello World";
    type: string

const constantString = "Hello World";
      type: "Hello World"

function printText(
  s: string, 
  alignment: "left" | "right" | "center"
) {}

function compare(
  a: string, 
  b: string
): -1 | 0 | 1 {
  return a === b ? 0 : a > b ? 1 : -1;
}