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by jemmyw 1256 days ago
If you're just looking for general feedback, constructor typing has made my life really hard trying to type an existing JS library. In a JS object instance like `const user = new User()` you can call `this.constructor.staticMethod()` and it calls `staticMethod()` on `User` or up the inheritance chain. But TS doesn't type `.constructor` so you're out of luck. In the simple case you call `User.staticMethod()` but that doesn't work for an instance method on a superclass that wants to call the method of the constructor of the instance.

I understand why JS makes this difficult to type because you can mess around with the constructor. But for normal every day code you just expect `this.constructor` on an instance of `User` to be `User` and it really sucks that it isn't!
1 comments
ryanwheale 1252 days ago
> you can call `this.constructor.staticMethod()` and it calls `staticMethod()` on `User` or up the inheritance chain.

This is where I have come to like typescript. 4 years ago, I would have agreed with you, but TS have moved me into a world where I wouldn't write that kind of code any more, and it honestly makes me sick to look at.

Instead I would just do `User.staticMethod` because this accomplishes several things:

  - super classes shouldn't know about inheriting classes. If they do, TS gives you interfaces and abstract classes for this purpose.
  - it still crawls up the proto chain, so the inheriting class doesn't need to know about every super class
  - no risk in `this` pointing to something unintentional (if someone calls or apply's your method)
  - shorter code, easier to read IMO, especially for less experienced devs
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jemmyw 1250 days ago
I might agree with you but sometimes we have to type up JS code that is written in different styles to what we'd personally prefer. TS should (a) let me generate the types that are used in JS. There are areas like proxies where that's just not possible, but in this case it feels like there's a disparity between TS and JS over classes. (b) I want to work with this code in my editor without red lines all over the place on perfectly valid code.

super classes don't need to 'know' about the inheriting classes for static inheritance to work. i.e. here is a simplified problem in the library I'm trying to add types to:

superclass:

  static hasField(name) { return false }
  constructor() {
    if(this.constructor.hasField('id')) { ... }
  }
subclass:

  static hasField(name) { if(name === 'id') return true; }
(it doesn't really look like that but you get the idea). That just works in JS, but in TS you get `Property 'hasField' does not exist on type 'Function'`. In the TS definition there are a couple of ways I can trick it to return the right thing for `this.constructor` but if I'm looking at a JS file in vscode with TS' checkJs flag on then this pattern should just work in my opinion.

edit: And I don't think I should have to trick it, that makes the definition harder to read and essentially wrong somehow.

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