在打字稿中定义全新类型的最佳做法？

Question

I have an execution environment with several constants globally:

TOP = 1
TOP_RIGHT = 2
RIGHT = 3
BOTTOM_RIGHT = 4
BOTTOM = 5
BOTTOM_LEFT = 6
LEFT = 7
TOP_LEFT = 8

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It is clear to me that these 8 constants are not just arbitrary constants, but actually a set of directions. Therefore, I would like to have them be of the DIRECTION type, so that I can do things like this:

let test: DIRECTION = TOP_LEFT;
let foo: DIRECTION = TOP;
let bar: DIRECTION = LEFT;
let target: DIRECTION = RIGHT;

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I've considered several options for how to make this happen (ie what to put in the direction.d.ts file):

1. enum s require a ton of syntax & boilerplate to just get off the ground, so they are undesirable in this case.
2. When I use the type keyword, it seems unable to create a new type that is not simply an alias of another. (eg type DIRECTION=integer; is allowed, but type DIRECTION; is not. Defining DIRECTION as an alias of integer is undesirable because, despite the fact that they are technically integers in the environment, BOTTOM-2 is nonsensical, and should cause an error.
3. interface DIRECTION {} seems to result in the desired behavior, letting me define this new type. However, it seems like quite an abuse of the typing system (I am under the impression that TS's interfaces were basically the equivalent of classes.)

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What's the most TS-friendly way to accomplish this?

Answer 1

You can use const and type for this:

const TOP = 1
const TOP_RIGHT = 2
type DIRECTION = 1 | 2

let x: DIRECTION = TOP

However, I believe enum is a better solution for this purpose.

For example, this is valid but not desirable:

const ONE = 1
let x: DIRECTION = ONE

Answer 2

In reference to solution #1, as originally posted:

declare const enum Direction {
    TOP = 1,
    TOP_RIGHT = 2,
    RIGHT = 3,
    BOTTOM_RIGHT = 4,
    BOTTOM = 5,
    BOTTOM_LEFT = 6,
    LEFT = 7,
    TOP_LEFT = 8
}
declare const TOP=Direction.TOP
declare const TOP_RIGHT=Direction.TOP_RIGHT
declare const RIGHT=Direction.RIGHT
declare const BOTTOM_RIGHT=Direction.BOTTOM_RIGHT
declare const BOTTOM=Direction.BOTTOM
declare const BOTTOM_LEFT=Direction.BOTTOM_LEFT
declare const LEFT=Direction.LEFT
declare const TOP_LEFT=Direction.TOP_LEFT

Answer 3

In reference to idea #3, as posted above:

interface DIRECTION {}

declare const TOP: DIRECTION;
declare const TOP_RIGHT: DIRECTION;
declare const RIGHT: DIRECTION;
declare const BOTTOM_RIGHT: DIRECTION;
declare const BOTTOM: DIRECTION;
declare const BOTTOM_LEFT: DIRECTION;
declare const LEFT: DIRECTION;
declare const TOP_LEFT: DIRECTION;

This code is significantly more concise than the solution with enum .

I am still looking for ways to improve it, however, so suggestions/changes are welcome.