ES2015: Returning a Promise from a constructor — Warning: I'm fairly sure this is always an anti-pattern.

es2015-returning-from-constructor.js

class Parent {
  constructor() {
    return new Promise(resolve => {
      setTimeout(() => resolve({ data: 'important' }), 1e3);
    });
  }
}

class Child extends Parent {
  constructor() {
    return super().then(console.log);
  }
}

( new Parent() ).then(console.log);
//=> { data: 'important' }

( new Child() );
//=> { data: 'important' }