Export enums as const

[srchase]

Currently, enums as generated as the following:

export enum Suit {
  club = "club",
  diamond = "diamond",
  heart = "heart",
  spade = "spade",
}

This results in the following JavaScript:

var Suit;
(function (Suit) {
    Suit["club"] = "club";
    Suit["diamond"] = "diamond";
    Suit["heart"] = "heart";
    Suit["spade"] = "spade";
})(Suit = exports.Suit || (exports.Suit = {}));

With this PR, enums are now generated as the following:

export const /*enum*/ Suit = {
  club: "club",
  diamond: "diamond",
  heart: "heart",
  spade: "spade",
} as const;
export type Suit = typeof Suit[keyof typeof Suit];

Which results in this JavaScript:

exports.Suit = {
  club: "club",
  diamond: "diamond",
  heart: "heart",
  spade: "spade",
};

By exporting the additional type, compatibility is preserved for any consumers that are using the existing enums as types.

With the tsconfig removeComments setting set to true, the in-line /*enum*/ comment will be excluded from the transpiled JavaScript.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[syall]

Are there any backwards compatibility concerns around this?

[srchase]

Are there any backwards compatibility concerns around this?

I added the type export to allow for using these generated consts as types.

[syall]

In the example, it shows a double export of Suit, and was wondering if this is valid?

export const /*enum*/ Suit = { // <- Suit export 1
  club: "club",
  diamond: "diamond",
  heart: "heart",
  spade: "spade",
} as const;
export type Suit = typeof Suit[keyof typeof Suit]; // <- Suit export 2

In TS playground, the output of .d.ts is:

export declare const /*enum*/ Suit: {
    readonly club: "club";
    readonly diamond: "diamond";
    readonly heart: "heart";
    readonly spade: "spade";
};
export type Suit = typeof Suit[keyof typeof Suit];