micro-redux: a minimal implementation of Redux createStore, with thunkish behavior added in

micro-redux.js

/**
 * Minimal implementation of Redux createStore, with thunkish behavior.
 */
import subject from './micro-subject' // see micro-subject.js gist

/**
 * @template T
 * @typedef {import('./subject').Subject<T>} Subject
 */
/**
 * @param {(state: any, action: any) => any} reducer
 * @param {any} [initial]
 */
export const createStore = (reducer, initial) => {
  /**
   * @type {Subject<void>}
   */
  const _subject = subject()
  let state = initial !== undefined ? initial : reducer(undefined, {})

  return {
    /**
     * Dispatch an action to update the store.
     */
    dispatch(action) {
      // Built-in 'thunk' functionality.
      if (typeof action === 'function') {
        action(this.dispatch.bind(this), this.getState)
      } else {
        state = reducer(state, action)
        _subject.notify()
      }
    },

    /**
     * Get the store's current state.
     */
    getState() {
      return state
    },

    /**
     * Receive notifications when the store is updated.
     *
     * @param {() => void} observer
     *
     * @returns {() => void} unsubscribe function
     */
    subscribe(observer) {
      const unsubscribe = _subject.subscribe(observer)
      _subject.notify()
      return unsubscribe
    }
  }
}

export default createStore