Explicit typing for merging 2 objects/decorating in TypeScript with intersection types

settings-page.po.ts

import { $ } from 'protractor';

export interface ChangePasswordDialog {
  currentPasswordField: ElementFinder;
  incorrectPasswordError: ElementFinder;
  submitButton: ElementFinder;
}

export class SettingsPage extends AppPage {
  get changePasswordDialog(): ElementFinder & ChangePasswordDialog {
    const func: ElementFinder = $('app-reset-password-dialog');
    const addOns: ChangePasswordDialog = {
      get currentPasswordField() { return func.$('input[name="currentPassword"]'); },
      get incorrectPasswordError() { return func.$('.reset_password__incorrect-password'); },
      get submitButton() { return func.$('.password-dialog__confirm-button'); },
    };
    return Object.assign(func, addOns);
  }
}