Angular如何知道构造函数的类型是什么？

Question

I've been trying to replicate the way Angular interprets the constructor on an injectable service.

function Injectable() {
  return function<T extends { new (...args: any[]): {} }>(con: T) {
    return class extends con {
      static __constructorClasses: any[] = [];

      constructor(...args: any[]) {
        super(...args);
        Foo.__constructorClasses = ???;
      }
    };
  };
}

How can I return a list of classes into the Foo.__constructorClasses

class Bar {
  public hello = 'world';
}

@Injectable()
class Foo {
  constructor(private bar: Bar) {}
}

// I expect: Foo.__constructorClasses = [Bar]
const bar = new Foo.__constructorClasses[0]();
console.log(bar.hello) // 'world'

Am I going about this in the wrong way? My goal is to know (after converting to es2015+) what each of the classes are in the constructor. So that I either have the class itself [Bar] or a string representing the class 'Bar' . The string is also fine because I can use it to pull the Bar instance from a Proxy.

Answer 1

Utilizing:

• typescript: 3.5.3
• reflect-metadata: 0.1.13

Command to run:

tsc foo.ts --emitDecoratorMetadata --experimentalDecorators && node foo.js

foo.ts:

import 'reflect-metadata';

type Constructor<T> = { new (...args: any[]): T };

function Injectable() {
  return function _Injectable<T extends Constructor<{}>>(Base: T) {
    return class __Injectable extends Base {
      classes: any[] = Reflect.getMetadata(
        'design:paramtypes',
        __Injectable.prototype.constructor
      );

      constructor(...args: any[]) {
        super(...args);
      }
    }
  };
}

class Bar {
  label: string;

  constructor() {
    this.label = 'BarClass';
  }
}

@Injectable()
class Foo {
  constructor(private bar: Bar) {}
}

const bar = new Bar();
const foo = new Foo(bar);

//@ts-ignore // ts doesn't strictly know that classes exists on Foo
console.log(foo.classes); // [ [Function: Bar] ]
//@ts-ignore // ts doesn't strictly know that classes exists on Foo
console.log(new foo.classes[0]().label); // 'BarClass'

Most of the information was available here : https://www.typescriptlang.org/docs/handbook/decorators.html however I thought this quick example would more simply demonstrate how Typescript can emit the classes passed to a classes constructor.

Further Reading:

https://codeburst.io/decorate-your-code-with-typescript-decorators-5be4a4ffecb4 https://blog.thoughtram.io/angular/2015/09/17/resolve-service-dependencies-in-angular-2.html https://blog.wizardsoftheweb.pro/typescript-decorators-reflection/