TS mixin decoration

example.ts

class A {
  p1() {
    console.log('this is p1')
  }
}

class B {
  p2() {
    console.log('this is p2')
  }
}

class C {
  p3() {
    console.log('this is p3')
  }
}

@mixin(A, B, C)
class Child {}

const child = new Child()
child.p3()
child.p1()
child.p2()

// this is p3
// this is p1
// this is p2

class Foo {
  protected makeFoo() {
    return 'foo'
  }
}

class Bar {
  protected makeBar() {
    return 'bar'
  }
}

@mixin(Foo, Bar)
class FooBar {
  public makeFoobar() {
    return this.makeFoo() + this.makeBar()
  }
}

const fooBar = new FooBar()

console.log(fooBar.makeFoobar()) // foobar

mixin.ts

/**
 * A rigorous type alias for a class.
 */
type Class<CtorArgs extends any[] = any[], InstanceType = {}, StaticType = {}> = {
  new (...args: CtorArgs): InstanceType & { [K in keyof StaticType]: StaticType[K] }
}

/**
 * Mixin decoration implementation
 * @example @mixin(ClassA, ClassB, ClassC)
 *          class targetClass{}
 */
function mixin(...mixins: Class[]) {
  return (targetClass: Class) => {
    function copyProperties<T extends U, U extends object>(target: T, source: U): void {
      for (const key of Reflect.ownKeys(source)) {
        if (key !== 'constructor' && key !== 'prototype' && key !== 'name') {
          const desc = Object.getOwnPropertyDescriptor(source, key) as PropertyDescriptor
          Object.defineProperty(target, key, desc)
        }
      }
    }

    for (const mixin of mixins) {
      // 拷贝静态属性
      copyProperties(targetClass, mixin)

      // 拷贝原型属性
      copyProperties(targetClass.prototype, mixin.prototype)
    }

    // 拦截构造器方法，进行实例属性的拷贝
    return new Proxy(targetClass, {
      construct(target, args: any) {
        const obj = new target(...args)

        for (const mixin of mixins) {
          copyProperties(obj, new mixin())
        }

        return obj
      }
    })
  }
}