delegate.ts

delegate.ts

class EventEmitter {
  on(event: string, callback: () => void) {
    console.log(`EventEmitter#on`, this.constructor.name);
  }
  emit(event: string) {
    console.log(`EventEmitter#emit`, this.constructor.name);
  }
}
class Win {
  x:number = 41;
  y:number = 42;
  moveTo(x:number,y:number) {
    console.log(`Win#moveTo ${this.x}, ${this.y}`, this.constructor.name);
  }
  showDevTools() {
    console.log(`Win#showDevTools`, this.constructor.name);
  }
  closeDevTools() {
    console.log(`Win#closeDevTools`, this.constructor.name);
  }
  close() {
    console.log(`Win#close`, this.constructor.name);
  };
}

class NwWindow  {
  private win: Win = new Win();
  openDevTools() {
    console.log(`Win#openDevTools`, this.constructor.name);
    return this.win.showDevTools();
  }
}

// here is the key that make ts understand the inheritance and make code suggestion work as expected
interface NwWindow extends Omit<Win, 'showDevTools'>, EventEmitter {}

// delegate() make prototype chain work as expected in runtime
delegate<NwWindow>(NwWindow, [Win, EventEmitter], 'win'); 

function delegate<T extends {[key: string]: any}>(derivedCtor: any, constructors: any[], propName: string) {
  constructors.forEach((inherited) => {
    Object.getOwnPropertyNames(inherited.prototype).forEach((name) => {
      const desc = Object.getOwnPropertyDescriptor(inherited.prototype, name);
      if (desc && name !== 'constructor') {
        console.log(`Delegating ${name}`);
        const original = desc.value as Function;
        desc.value = function (...args: any) {
          const ptr = this as T;
          const prop = ptr[propName];
          return original.apply(prop, args);
        };
        Object.defineProperty(derivedCtor.prototype, name, desc);
      }
    });
  });
}


const w = new NwWindow();
console.log(w);
w.openDevTools();
w.closeDevTools();
w.on('a', console.log);
console.log(w);