Immer Store

immerStore.ts

import { writable, Readable } from 'svelte/store';
import { produce, enableAllPlugins } from 'immer';

enableAllPlugins();

export interface ImmerStore<T> {
  update: (updateFn: (draft: T) => T | void) => T;
  subscribe: Readable<T>['subscribe'];
}

export default function immerStore<T = any>(initialValue: T): ImmerStore<T> {
  let store = writable<T>(initialValue);

  let update = (updateFn: (draft: T) => T | void) => {
    let ret;
    store.update((value) => {
      ret = produce(value, updateFn) as T;
      return ret;
    });

    return ret;
  };

  return {
    update,
    subscribe: store.subscribe,
  };
}

The idea behind Immer is to keep the objects immutable while retaining the convenience of mutable-style code.

Yes, that's exactly what I have in mind. I wish it could be almost transparent to work with stores in an immutable way, that's why I asked about auto-subscription support. Also, getting rid of the $i = $i would be nice, it still brings visual noise to my eyes.

I think that if it gets polished, an immutable store would be a great addition to svelte's arsenal.