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Comment by skrebbel | Hacker News Reader

Yep, and nowadays TS has string literal types and unions so enums are pretty much obsolete.

    type Direction = "up" | "down";

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Enums and string literals aren't completely interchangable.

Enums are transpired to objects so you can iterate the keys/values. You can't do that with SL which are a transpiler feature only.

Also you can't codedoc string literal values like you can with enums where it shows up with intellisense.

I tend to prefer enums as a result

Since TS 3.4 you can have enum-like behaviour by using the `as const` annotation on object and array literals.

    const types = ['x', 'y', 'z'] as const;
    const a: typeof types[number] = 'a'; // not ok
    const b: typeof types[number] = 'z'; // ok

Not to be confused with `const enum` which act more like a preprocessor and emits in the value at compile time.

    const enum Directions { Up, Down, Left, Right }
    console.log(Directions.Left)
    // emits js file with console.log(2)

https://www.typescriptlang.org/docs/handbook/enums.html#cons...

That is correct. However, I still prefer using union types so that I'm not locked in to TypeScript.

By using only union types as "enums" and never using enums or namespaces, I guarantee that all the TS-specific code I write can be erased and if I ever were to use just JavaScript in the future, I could.

Also, I use Babel to transpile TS to ES3.

You can have the best of both worlds, see this comment https://news.ycombinator.com/item?id=21134911

Interesting. I swear that when I previously tried this approach I had to explicitly tell typescript that a string is indeed of a particular type:

  const test(direction: Direction) => direction;
  test('up' as 'up');

But now that I'm testing in typescript playground, I no longer need to write the "as" part — simply `test('up');` works fine as well.

I wonder if you've seen this quirk of typescript before.

I have.

It's when you do

    const dir = "up"; // TS infers type "string"
    test(dir); // error

For mutable variables (let/var), you usually want TS to infer `string` in the first line. IMO the fact that they also infer `string` for constants is a design flaw, that I hope will one day be fixed.

They recently added a feature to make this less painful:

    const dir = "up" as const;
    test(dir); // works

That's the same as `as "up"` bit without having to duplicate the string.

`const` variables are actually inferred without widening. So in your example `dir` would be inferred as `"up"`, not `string`. If you use `let` (or `var`) however that would be true.

My god, you are right!

(example in typescript playground: https://www.typescriptlang.org/play/#code/C4TwDgpgBAIglgJwgY...)

Oh wow! Great, thanks. I wonder how I recalled that wrong.

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