Potential $effect.server rune?

[peterreeves]

I've had a few projects recently using adapter-node where I'm using either streaming requests or websockets, and when state changes I need to push updates to connected clients. I get all excited to use runes, before remembering that $effect and $effect.root don't run on the server 🥲. I'm currently using old subscriber functions instead, and it's a much worse experience (It really shows how nice runes are by comparison!).

I've been wondering if it would be possible (or even a good idea?) to create an $effect.server rune. I imagine it using it like this:

class MyServerState {
    count = $state(0);
    connectedClients = new Set();
    disposeEffect = null;

    constructor () {
        this.disposeEffect = $effect.server(() => {
            for (const conn of this.connectedClients) {
                conn.sendData(this.count);
            }
        });
    }
    
    dispose = () => {
        this.disposeEffect.?();
        for (const conn of this.connectedClients) {
            conn.disconnect();
        }
        connectedClients.clear();
    }
}

const serverState = new MyServerState();

// Elsewhere ...
serverState.connectedClients.add(clientConnection);
serverState.count += 1;

It would ONLY run on the server, and it returns a dispose function just like $effect.root, so it would not need to be wrapped in a root like $effect does. This probably wouldn't be a good idea for platforms that aren't adapter-node, so I guess in those cases it might get transformed into a no-op?

Still not sure if it's a great idea. $effect is already a footgun so adding another effect rune shouldn't be done carelessly, but it would be really nice to be able to have server-side reactivity with runes 😅