Why was it decided that we should have to write:

class Foo {
    constructor() {
        return new Promise(async (resolve, reject) => {
            this.sync = 123;
            this.async = await someAsyncCall();
            resolve(this);
        });
    }
}

instead of just

class Foo {
    async constructor() {
        this.sync = 123;
        this.async = await someAsyncCall();
    }
}

works for me, just needs to be a little different from sync subclassing, which a dedicated syntax sugar could do

class Bar extends Foo {
    constructor() {
        return new Promise(async (resolve, reject) => {
            const base = await super();
            base.barSync = 123;
            base.barAsync = await someAsyncCall();
            resolve(base);
        });
    }
}

It's the same for normal properties:

class Bar extends Foo {
    prop = 2;
    constructor() {
        return new Promise(async (resolve, reject) => {
            const p = super();
            console.log(p.prop); // 2
            const base = await p;
            resolve(base);
        });
    }
}

TIL:

new class {
  "constructor"() { console.log("hi") } // logged
}
new class {
  ["constructor"]() { console.log("hi") } // not logged
}

Similar to["__proto__"] vs "__proto__"