TypeScript - Enums

An enum is a special "class" that represents a group of constants (unchangeable variables).

Numeric Enums - Default

By default, enums will initialize the first value to 0 and add 1 to each additional value:

enum Directions { North, East, South, West }
let currentDirection = Directions.North;
console.log(currentDirection); // 0
currentDirection = 'North'; // throws error as 'North' is not a valid enum

Numeric Enums - Initialized

You can set the value of the first numeric enum and have it auto increment from that:

enum Directions { North = 1, East, South, West }
console.log(Directions.North); // 1
console.log(Directions.West); // 4

Numeric Enums - Fully Initialized

You can assign unique number values for each enum value. Then the values will not incremented automatically:

enum StatusCodes {
  NotFound = 404,
  Success = 200,
  Accepted = 202,
  BadRequest = 400
}
console.log(StatusCodes.NotFound); // 404
console.log(StatusCodes.Success); // 200

String Enums

Enums can also contain strings. This is more common than numeric enums, because of their readability and intent.

enum CardinalDirections {
  North = 'North',
  East = "East",
  South = "South",
  West = "West"
};
console.log(CardinalDirections.North); // "North"
console.log(CardinalDirections.West); // "West"