Enumerations

Enumerations allow us to define a set of named constants. Since the TypeScript 2.4 release, these named constant values can be string values. Originally, they could only be numeric values:

enum CardinalDirection {
    Up,
    Down,
    Left,
    Right
}

A common workaround to this limitation was the usage of union types of literal types:

type CardinalDirection =
    "North"
    | "East"
    | "South"
    | "West";


function move(distance: number, direction: CardinalDirection) {
    // ...
}

move(1,"North"); // Okay
move(1,"Nurth"); // Error!

Since the TypeScript 2.4 release, enumerations with string values are also supported:

enum CardinalDirection {
    Red = "North",
    Green = "East",
    Blue = "South",
    West = "West"
}