Async Constructor Helper in JavaScript

example.js

function WillBe(Class){
  return class AsyncConstructor extends Class {
    constructor(...values) {
      super(...values);
      this.willBe = (async () => { 
           let resolvedThis = await promiseAllObj(this);
           //Remove this.willBe to avoid circular promises
           return Object.keys(resolvedThis)
                  .reduce((acc,key) => (key === 'willBe' 
                  ? acc 
                  : {...acc, [`${key}`]: resolvedThis[key]}
                  ), {})
            })()
    }
    get init(){
      return this.willBe.then(instance => {
        this.value = instance;
        return this;
      })
    }
  }
}

const Asyncio = WillBe(class Bar {
   constructor(foo, baz) {
    this.foo = foo;
    this.bar = fetchBar()
    this.baz = baz;
   }
})


const example = new Asyncio('sync foo', 'sync baz')
// logs 'sync foo'
console.log(example.foo)
// logs 'sync baz'
console.log(example.baz)


async function main(){
  let {value} = await example.init
	// logs {foo: 'sync foo', bar: 'async bar', baz: 'sync baz'
    console.log(value)
}
main()


// ********Helpers**************

function promiseAllObj(obj){
  return Promise.all(
         Object.entries(obj)
        .map(([key, val]) => 
        val instanceof Promise 
        ? val.then(res => [key, res])
        : new Promise(res => res([key,val])))
        )
        .then(Object.fromEntries)
}

function fetchBar() {
  return new Promise((res,rej) => setTimeout(() => res('async bar'), 2000))
}