Async JS constructor via static "create" method – TypeScript types problem

Question

I am working on the universal abstraction/base of the async constructor and it works fine with JavaScript.

But I'm stuck with correct TypeScript types, it should work like this:

const a: AnyClass = await AnyClass.create();

It works fine in JavaScript, but TypeScript types are wrong (missing at the moment).

Example of the similar class called DbConnection:

class DbConnection extends AsyncConstructor<[serverId: number, url: string]> {
    #serverId: number;
    #connection: Connection;

    protected constructor(serverId: number, url: string) {
        super(serverId, url);
        this.#serverId = serverId;
    }

    protected override async constructorAsync(serverId: number, url: string): Promise<void> {
        this.#connection = await DB.connect(url);
    }
}

The base class is:

class AsyncConstructor<CtorParams extends any[]> {
    protected constructor(...args: CtorParams) {}

    protected async constructorAsync(...args: CtorParams): Promise<void> {
        return Promise.resolve();
    }

    // =-->>> MISSING TYPES FOR THE NEXT METHOD: <<<--=
    static async create(...args: CtorParams) {
        const res = new this(...args);
        await res.constructorAsync(...args);
        return res;
    }
}

What type to specify for the return of the create method?

@jonrsharpe not really, since it doesn't provide any solution, at least partial. Also JavaScript version works perfectly. — Oleg Zarevennyi
– Oleg Zarevennyi, Commented Feb 22, 2024 at 15:00
I didn't say it provided a solution, I said it was related. The comment from jcalz explains why there likely isn't (or at least wasn't) a solution. And whether or not the JS works isn't the question - TS disallows plenty of things that work in JS, usually on purpose. — jonrsharpe
– jonrsharpe, Commented Feb 22, 2024 at 15:04
This comment on the github issue that's linked describes a factory method as well: github.com/microsoft/TypeScript/issues/… Immediately above that comment is a solution with generics that's a little verbose but it might do the trick. — KernelDeimos
– KernelDeimos, Commented Feb 22, 2024 at 16:27
"not possible to have interface that requires static members" - not during the inheritance/implements declaration, but it is possible to require them during the create invocation. Have a look at stackoverflow.com/a/72771370/1048572 for example. Here, it could be something like async create<T>(this: { new(c: Connection): T; createConnection(): Promise<Connection> }): T { return new this(await this.createConnection()); } — Bergi
– Bergi, Commented Mar 3, 2024 at 22:13

Oleg Zarevennyi · Accepted Answer · 2024-03-03 10:41:26Z

This is impossible as of 2024.02 due to the limitation of the TypeScript (for sure <= v.5.3)

As suggested by @KernelDeimos there is an open issue at the TypeScript repository - Polymorphic "this" for static members #5863
And by @jonrsharpe there is "similar" problem described here - Using `this` as a generic type on a static method

The only possible partial solution as for now is:

class DbConnection  {
    #serverId: number;
    #connection: Connection;

    static async create(serverId: number, url: string): Promise<DbConnection> {
        const connection = await DB.connect(url);
        const res = new DbConnection(serverId, url, connection);        
        return res;
    }

    protected constructor(serverId: number, connection: Connection) {        
        this.#serverId = serverId;
        this.#connection = connection;
    }
}

The disadvantage of this approach is that you:

cannot force some classes to follow the same implementation
as a result, each class may have its unique name and way of creation
this may cause problems during the inheritance of complex classes, especially with the big code base

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