Redux style store with svelte/store

svelte-store.js

/**
 * Svelte does not compare objects
 * https://github.com/sveltejs/svelte/issues/2171
 * and therefore store.update notifies subscribers, even if same object is
 * returned. Otherwise the method could be much simpler:
 * const dispatch = action => update(state => reducer(state, action));
 *
 * @param {function} reducer
 * @param {*} initialState
 */
export function createStore(reducer, initialState = {}) {
  const store = writable(initialState);

  const dispatch = action => {
    const current_state = get(store);
    const next_state = reducer(current_state, action);

    if (current_state !== next_state) {
      store.set(next_state);
    }
  };

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

Simple Usage

<script>
import { createStore } from './svelte-store.js';
const ACTION_INCREASE = 0;
/* const ACTION_DECREASE = 1; */

function storeReducer(state, action){
    switch(action){
        case ACTION_INCREASE:
            return state + 1;
    }

    return state;
}

const store = createStore(storeReducer, 1);
store.dispatch(ACTION_INCREASE);
</script>

<div>value is {$store}</div>