类型在 TypeScript 中定义一个枚举

Question

I have a TypeScript Enum that lives within a different namespace to the file I am trying to use it in. The namespace for now unavoidable reasons is long and cumbersome to write

The project is not using modules and does not have a module loader so no imports or exports. My hands are tied here unfortunately. We bundle files manually.

enum Movement {
    run,
    walk
}

function Move(movement: App.System.User.Area.Movement) { 
    if (movement === App.System.User.Area.Movement.run) { //... }
    //....
}

I am able to use it seems the type keyword to (and I am not sure this is the TypeScript word for it) type def that long namespace away.

type MovementType = App.System.User.Area.Movement;
function Move(movement: MovementType) { 
    if (movement === App.System.User.Area.Movement.run) { //... }
    //....
}

But I cannot use that type def'd type in the equals comparison in my function above because "MovementType only refers to a type but is being used as a value here" when I try to do:

type MovementType = App.System.User.Area.Movement;
function Move(movement: MovementType) { 
    if (movement === MovementType.run) { //... }
    //....
}

Is there any way to get around this? Why can't I use it in the conditional statement while I can have it as a parameter? How can I get around my very long namespace?

---

I am currently using TypeScript 3.1

Answer 1

As Pac0 mentioned, an enum is both a set of values and a type. If the import solution doesn't work for you, you could try aliasing both the type and value.

type MovementType = App.System.User.Area.Movement;
const Movement = App.System.User.Area.Movement;
function Move(movement: MovementType) { 
    if (movement === Movement.run) { //... }
    //....
}

Example on TypeScript Playground

Answer 2

The type keyword is indeed only creating an alias for the type that is defined by the enum , it can't work to access the values of the enum (hence, the explicit error messages).

You can achieve something similar to what you want by aliasing the long namespace with import :

import area = App.System.User.Area;

function Move(movement: area.Movement) { 
    if (movement === area.Movement.run) { //... }
    //....
}

That should at least help a bit.

More info in TypeScript docs .

Example on TypeScript playground