exporting enum from typescript type definition file

Question

I'm writing the type definitions for a library I'm using. One function in the library identifies the mouse button clicked by an integer:

 //index.d.ts  export as namespace myLib;  // activates the library listening for a specific mouse button  function activate(button : number ) : void  

I introduced an enum to make this nicer:

//index.d.ts export as namespace myLib; export enum MouseButton {     LEFT = 1,     MIDDLE = 2,     RIGHT = 4 }  export function activate(button : MouseButton ) : void; 

Now, when I import this function and use it, everything compiles but I guess the enum is stripped and undefined when executed in the browser. The error message says Cannot read property 'LEFT' of undefined.

Therefore I rearranged the files like so:

//MouseButton.ts export enum MouseButton {     LEFT = 1,     MIDDLE = 2,     RIGHT = 4 }  //index.d.ts export as namespace myLib; import {MouseButton} from MouseButton; export {MouseButton} from MouseButton; export function activate(button : MouseButton ) : void; 

Now I can import {MouseButton} from "myLib/MouseButton"; import * as myLib from "myLib". But this requires two imports. Referencing myLib.MouseButton still compiles but doesn't run.

Is there any way to import and reference the MouseButton enum via the myLib imported via the import * as myLib statement? I'm not only looking for an answer explaining how to do it but for one explaining why my solution doesn't work or why it isn't possible. Hints to resources explaining what's wrong are also appreciated

PS: I also tried the syntax suggested here re-export Typescript enum from namespace? but that didn't work either.

PPS: The module in question is a UMD module from the cornerstone project (https://github.com/cornerstonejs/cornerstone) used in an angular 6 project.

Answer 1

(To complete t.animal's own answer)

Declaration files are difficult to make: see the long documentation. Sometimes looking in existing .d.ts files can help.

Regarding enum, declaring them as const enum is a clean and simple approach. It's what is done for jquery for instance, see @types/jquery/index.d.ts for Mouse and Key. It's handy because standard enums are compiled in JavaScript as arrays while const enum members are compiled directly as values ; see TypeScript Playground.

Answer 2

Solved it by the help of Romain Denau's comment above. It nudged me in the right direction: What code does the typescript compiler generate from an enum (see https://www.typescriptlang.org/docs/handbook/enums.html#enums-at-runtime)? Declaring the enum const allows the typescript compiler to completely swap the identifier with the respective value, effectively inlining it. No more leakage of the enum into the production code. Thanks!

//index.d.ts export as namespace myLib;  export const enum MouseButton {     LEFT = 1,     MIDDLE = 2,     RIGHT = 4 }  export function activate(button : MouseButton ) : void;