Is there any way to check if an object is a type of enum in TypeScript?

Question

enum Direction {
    Up = 1,
    Down,
    Left,
    Right
}

if (typeof Direction === 'enum') {
    // doesn't work
}

Any way to check if the above is in fact an enum?

Answer 1

Enums are compiled into simple objects that have two way mapping:

name => value
value => name

So the enum in your example compiles to:

var Direction;
(function (Direction) {
    Direction[Direction["Up"] = 1] = "Up";
    Direction[Direction["Down"] = 2] = "Down";
    Direction[Direction["Left"] = 3] = "Left";
    Direction[Direction["Right"] = 4] = "Right";
})(Direction || (Direction = {}));

So the typeof of Direction is a plain "object".
There's no way of knowing in runtime that the object is an enum, not without adding more fields to said object.

---

Edit

Sometimes you don't need to try to workaround a problem with a specific approach you have, you can maybe just change the approach.
In this case, you can use your own object:

interface Direction {
    Up: 1,
    Down: 2,
    Left: 3,
    Right: 4
}
const Direction = {
    Up: 1,
    Down: 2,
    Left: 3,
    Right: 4
} as Direction;

Or:

type Direction = { [name: string]: number };
const Direction = { ... } as Direction;

Then turning this object into an array should be simple.