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by IggleSniggle 1085 days ago
The Reflect.defineMetadata API and the long-supported decorators syntax come from very early versions of Typescript when Typescript was (maybe) more actively trying to steer the direction of ECMAScript by implementing features that were Stage 2 proposals.

Typescript only got official ECMAScript decorator support in the recent v5. ECMAScript decorators only got to stage 3 in April ‘22.

But decorator syntax is just a kind of syntax sugar over passing a function through another function, and you can do that today to achieve runtime type information (see zod etc). Zod could be rewritten using decorator syntax and still be “just JavaScript” while providing compile-time type support.

The distinction being that supporting ECMAScript features is a goal for Typescript, but they were perhaps too aggressive early on in investing in decorators and the Reflect Metadata API. They had the wisdom to put these behind “experimental” flags, but I think they got quite popular within the typescript community due to the early adoption of both Typescript and both those features by Angular, which was really the only major lib using TS for quite some time.
1 comments
tentacleuno 1085 days ago
> Typescript only got official ECMAScript decorator support in the recent v5. ECMAScript decorators only got to stage 3 in April ‘22.

Yah, they've been out for ages. It's quite surprisingly how 1. long it's taken ECMA and 2. how quickly TypeScript took advantage of decorator syntax to improve TypeScript. I'd say it's a definite win for us people who love decorators.

> But decorator syntax is just a kind of syntax sugar over passing a function through another function, and you can do that today to achieve runtime type information

I'll have a look at Zod, thank you! I have to admit I like the simplicity of decorators; I'm playing with Dependency Injection and, while the loss of parameter injection is a bit disappointing, there are ways to work around it, e.g.

   @Injectable([Dependency])
   class Service {
     constructor (private dependency: Dependency) { } 
   }
> [...] features by Angular, which was really the only major lib using TS for quite some time.

Definitely. Although it'd be interesting to see how Angular handles the transition away from parameter injection; there's an open issue about it on their GitHub, but from what I can see none of the core members have spoken about it yet. <https://github.com/angular/angular/issues/50439>

The main proposal from a community member is to replace them with the Service Locator pattern (ew). Thankfully someone in-thread provided them with a little wisdom regarding why that's a terrible idea. Here's hoping Angular keeps a nice API.

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