Mastering TypeScript 3 - Third Edition

Enums

Enums are a special type that has been borrowed from other languages such as C#, C++, and Java, and provides a solution to the problem of special numbers. An enum associates a human-readable name for a specific number. Consider the following code:

enum DoorState { 
    Open, 
    Closed, 
    Ajar 
} 

Here, we have defined an enum called DoorState to represent the state of a door. Valid values for this door state are Open, Closed, or Ajar. Under the hood (in the generated JavaScript), TypeScript will assign a numeric value to each of these human-readable enum values. In this example, the enum value DoorState.Open will equate to a numeric value of 0. Likewise, the enum value DoorState.Closed will equate to the numeric value of 1, and the enum value ...