eslint-plugin-typescript-enum

eslint-plugin-typescript-enum

ESLint rules for TypeScript enums.

Motivations

From TypeScript Handbook on Enums:

Enums are one of the few features TypeScript has which is not a type-level extension of JavaScript.

In other words, TypeScript enums have their corresponsing runtime representations, they are not erased from your emitted JavaScript files after being compiled. This conflicts with one of the TypeScript Design Non-goals:

Provide additional runtime functionality or libraries. Instead, use TypeScript to describe existing libraries.

Having this TypeScript feature extending into your compiled JavaScript also conflicts with the TypeScript slogan of being a typed superset of JavaScript, which further introduces vendor lock-in.

Orta Therox from Typescript team mentioned in one of his YouTube videos that the TypeScript team actually regrets some of the changes it made in the beginning, including introducing enums which basically add features to JavaScript.

Moreover, using enums in TypeScript has a lot of caveats and edge cases to keep in mind. Some aspects of it are even considered not type safe!!! Head over to these wonderful articles for more details on these issues:

• https://maxheiber.medium.com/alternatives-to-typescript-enums-50e4c16600b1
• https://stackoverflow.com/questions/40275832/typescript-has-unions-so-are-enums-redundant/60041791#60041791

Additionally, if you have been using @babel/plugin-transform-typescript, you might have already noticed that one of the important caveats is to avoid using const enums, as those require type information to compile.

Nonetheless, TypeScript is undoubtedly a very fantastic programming language with an extremely powerful type system. Enums may have been a very good feature to have back in the early days (2011) when good alternatives did not yet exist.

We now already have much better alternatives than enums, such as const assertions, string unions, discriminated union, etc. Which is why I created this ESLint plugin to provide you with some handy configs and rules to disallow the use of TypeScript enums.

This article provides a very in-depth exploration on the alternatives to TypeScript enums:

• https://2ality.com/2020/02/enum-alternatives-typescript.html

Last but not least, as stated in Objects vs Enums section of TypeScript Handbook on Enums:

In modern TypeScript, you may not need an enum when an object with as const could suffice.

The biggest argument in favour of this format over TypeScript’s enum is that it keeps your codebase aligned with the state of JavaScript, and when/if enums are added to JavaScript then you can move to the additional syntax.

Installation

First, install the peer dependencies:

npm install --save-dev eslint typescript @typescript-eslint/parser

Next, install this package:

npm install --save-dev eslint-plugin-typescript-enum

Usage

Recommended Config

Configure this plugin in your ESLint configuration file (.eslintrc.js), this will disallow the use of enums altogether:

module.exports = {
  parser: "@typescript-eslint/parser",
  plugins: ["typescript-enum"],
  extends: ["plugin:typescript-enum/recommended"],
};

Babel Config (Not Recommended)

If you are using @babel/plugin-transform-typescript and want to allow the general use of enums except const enums:

module.exports = {
  parser: "@typescript-eslint/parser",
  plugins: ["typescript-enum"],
  extends: ["plugin:typescript-enum/babel"],
};

Rules

Key: :heavy_check_mark: = recommended, :wrench: = fixable, :thought_balloon: = requires type information

Name	Description	:heavy_check_mark:	:wrench:	:thought_balloon:
typescript-enum/no-const-enum	Disallow TypeScript const enums
typescript-enum/no-enum	Disallow all types of TypeScript enums	:heavy_check_mark:

Contributing

Feel free to suggest new configs and rules, PRs are also welcomed!