Enums

Enums are named constants and can really help with code readability.

They are by default 0 based numbers, but it's possible to define the number itself:

enum Control { Up, Down, Left, Right, Space } // 0 based
enum Letter { A = 97, B, C, D } // starts with 97, B will be 98

Or the value (using strings):

enum Direction {
  Up = 'VK_ARROW_UP',
  Down = 'VK_ARROW_DOWN',
  Left = 'VK_ARROW_LEFT',
  Right = 'VK_ARROW_RIGHT'
}

Advanced uses

🚀 Typescript enums can have dynamically initialized values:

enum Week {
  NumberOfDays = 7,
  Today = (new Date()).getDay() // today is saturday, so it would be 6
}

🚀 Number based enums have reversed mapping too:

• Week.NumberOfDays is 7
• Week[7] is "NumberOfDays"

🚀 Const enums are replaced inline by the compiler:

//                    0       1       2
const enum States { Select, Search, Result }

let getState = () => States.Search; // will be replaced with the raw value
assert.equal(getState.toString(), '() => 1'); // the stringified compiled javascript code