Async constructors for JavaScript

app.js

// In JavaScript, constructors can only be synchronous right now. This makes sense
// from the point of view that a constructor is a function that returns a newly
// initialized object.
//
// On the other hand, it would sometimes be very handy, if one could have async
// constructors, e.g. when a class represents a database connection, and it is
// desired to establish the connection when you create a new instance.
//
// I know that there have been discussions on this on StackOverflow & co., but
// the so-far mentioned counter arguments (such as: doesn't work as expected
// with new) didn't convince me. Actually, it works as expected (see below),
// as long as you use await – but this is true for any async function ;-)
//
// Could this be an idea for TC39?

'use strict';

const { promisify } = require('util');

const sleep = promisify(setTimeout);

class Example {
  // This is what I would like to have.
  // async constructor () {
  //   await sleep(1000);
  //   this.value = 23;
  // }
  
  // This is how it could be implemented.
  constructor () {
    return new Promise(async (resolve, reject) => {
      try {
        await sleep(1000);
        this.value = 23;
      } catch (ex) {
        return reject(ex);
      }
      resolve(this);
    });
  }
}

(async () => {
  // It works as expected, as long as you use the await keyword.
  const example = await new Example();

  console.log(example instanceof Example);
  console.log(example.value);
})();