Is it possible in Typescript to iterate over a const enum?

Question

Similar to this question, but with the enumeration marked as a constant: How do you go about iterating or producing an array of from the const enum?

Example

declare const enum FanSpeed {
    Off = 0,
    Low,
    Medium,
    High
}

Desireable Results

type enumItem = {index: number, value: string};
let result: Array<enumItem> = [
    {index: 0, value: "Off"}, 
    {index: 1, value: "Low"}, 
    {index: 2, value: "Medium"}, 
    {index: 3, value: "High"}
];

Answer 1

No, this is not possible with a const enum. Let's start with your original enum and log one of its values:

const enum FanSpeed {
    Off = 0,
    Low,
    Medium,
    High
}

console.log(FanSpeed.High);

The TypeScript compiler inlines all the references to FanSpeed, and compiles the above code into something like this:

console.log(3 /* High */);

In other words, since you're using a const enum, no FanSpeed object actually exists at run time, just simple numeric literals are passed around instead. With a regular, non-const enum, a FanSpeed would exist as a value and you could iterate over its keys.

Edit: If you can change the compiler settings of your project, see Titian's answer below for very useful information about the preserveConstEnums flag, which will cause a FanSpeed object to actually be created and thus give you a way to iterate over your enum.