Don't use Enums in Typescript, they are very dangerous 😨

ENUMs generate additional code at compile time, which increases the size of the final file.

This is a rather strange statement considering that typescript always generates more code than you write.

Good article!👏

You could also use enums in combination with interfaces, types of classes to encapsulate the behaviour of the enum, but, to be honest, I don’t really see a usage of an enum. You have far better solutions which are type safer such as string literals:

type Roles = 'admin' | 'writer' | 'reader';

This adds the benefit of preventing typos because that allow you to match the exact string value that is desired to be used. You have other better solutions as well, but this one should be a good one to replace the usage of an enum.

I prefer unions. More portable, you still get auto-complete and they are compiled away from the code into types only, without ever reaching the JavaScript output.

Great article!
If you write export const enum you won't generate single value.
And it will compile to nothing and in thee code it will have the hard code value

export const enum Enum {
FIRST = 'name'
}

I like the string Enum approach and I haven't face those issues when trying to use the real string instead of the enum key.

If you need to explicitly pass the string, you can use "as" to force its mapping. It will map perfectly with the string value of your enum.
I know we should avoid using "as", but it's a very unlikely situation (I can't think in a use case to explicitly pass a string if I have the enum keys).

I think the most common use case will be to match data received from the backend (string) with the frontend enum type. But just using "as" will map perfectly.

Based on the example in the article:

// frontend enum (the string value is the same used by the backend)
enum Roles {
  Admin = 'admin',
  Writer = 'writer',
  Reader = 'reader'
}

// frontend type definition
type User {
  id: string;
  name: string;
  role: Roles;  // defined using the frontend enum
}

// So, for a function with this enum as argument
declare function hasAccess(role: Roles): void;

hasAccess('admin') // Invalid
hasAccess('admin' as Roles) // Valid  (but very unlike to happen)
hasAccess(Roles.Admin) // Valid

// For a backend response mapping:
const userDto = await getUser();

const myUser: User = {
  id: userDto.id,
  name: userDto.name,
  role: userDto.role as Roles,  // the most common case
}

And by using enums instead of "objects as const", I don't need to do things like RoleKeys = typeof Roles[keyof typeof Roles] just to be able to use it.

As you can see enums are a named type and only accept enum-specific values, not compatible or similar values, which can lead to compatibility issues and should be carefully considered when designing and using enums.

Well, i.e. in the paragraph above, you write how bad it is that the typescript does not check that the value is in the range of the Enum. And here you write how to make it possible for strings, which will eventually lead to the same problems in the future as in the previous example.

In short, using objects or types instead of ENUMs is a better option in terms of flexibility, scalability, clarity, readability, and security.

May be you share examples in post?

I find it funny that experts recommend not using enums. We would have to see who these experts are, where they recommend not using enums and what they argue about it.

In my humble opinion, and point by point, one can argue against the "disadvantages" that the author of the article exposes:

1. Enums increase the weight of the build because they produce code. Obviously, because enums are translated into objects when compiling. This is by design and thanks to that you can iterate over the properties of an enum, for example: Object.keys(MyEnum).map(...). Of course replacing them with normal objects is not going to make the build weigh less XDDD.

2. Numeric enums are not type-safe. Correct, more or less and if you use them wrong (as in the example passing a number instead of using the enum you are defining). At compile time you don't have to write like this if you want TS to validate you (and whoever reads your code doesn't hate you). At runtime this can occur like any TypeScript violation (because it doesn't exist at runtime). If you don't like the quirks of numeric enums, the solution is not to use numeric enums. They have other disadvantages such as each value produces two entries in the compiled code, one for the value and one for the name. This does increase the weight of the build and is susceptible to producing errors when iterating as in the previous point. Could we say that experts recommend not using numeric enums? Maybe, but I wouldn't even dare, because they have their niche.

3. Valid strings such as "admin" cannot be passed instead of Roles.Admin. Goodness! Thanks to this you can't screw up like in point 2 with the numbers. Source code is clearer and less prone to errors when you are clear about what you are using. If you want to pass strings, don't use enums. If you want to use enums, don't pass strings. Roles.Admin is not the same as "admin".

Regarding the "solution": I think that allowing two ways of writing the same thing complicates the code without providing any advantage. In my opinion (I suppose a non-expert for the author of the article) it is better to use enums for this case and not allow strings.** If you want to use strings, don't use enums. If you want to use enums, don't use strings**. :-)

I found another solution, which looks a bit more elegant to me:

type EnumValues<E extends string> = `${E}` | E;

const enum RoleTypes {
    Admin = 'admin',
    Writer = 'writer',
    Reader = 'reader'
}

type Roles = EnumValues<RoleTypes>

declare function hasAccess(role: Roles): void;

hasAccess('admin') // valid
hasAccess(RoleTypes.Admin) // valid

What is the purpose of enum existence, then?

what do you do when someone fat fingers

const Roles = {
  Admin: "admin",
  Writer: "admin", // oops
  Reader: "reader"
} as const;