Mastering TypeScript 3 - Third Edition

Enum implementation

When TypeScript generates the JavaScript for enums, it uses the closure and Immediately Invoked Function (IIF) patterns to define a JavaScript object with the correct properties that can be used as an enum. Let's take a look at this implementation. Given our DoorState enum, which is defined as follows:

enum DoorState { 
    Open, 
    Closed, 
    Ajar 
} 

We know that we can reference the DoorState.Open value, which will be represented as a numeric value of 0, Closed as 1, and Ajar as 2. But what happens if we reference an enum using an array-type syntax, as follows:

var ajarDoor = DoorState[2]; 
console.log(`ajarDoor is : ${ajarDoor}`); 

Here, we assign the variable ajarDoor to an enum value based on the second index value of the DoorState ...