kilto/src/createStore.js

A state management system with easy async and low boilerplate.

'use strict';
import isPromise from './util/isPromise';

// TODO: middleware support

export default function createStore(initialState) {
  let state = initialState;
  const subscribers = [];

  const getState = () => state;

  const updateState = (newState) => {
    if (newState === state) return state;
    state = newState;
    
    subscribers.forEach((subscriber) => {
      subscriber(state);
    });

    return state;
  };

  const unsubscribe = (cb) => {
    const i = subscribers.indexOf(cb);
    if (i > -1) {
      subscribers.splice(i, 1);
    }
  };

  const subscribe = (cb) => {
    subscribers.push(cb);
    return () => unsubscribe(cb);
  };

  const dispatch = (actionsArg, ...args) => {
    if (actionsArg === null || actionsArg === undefined) {
      throw new TypeError('The first argument of dispatch must be a function or array.');
    }
    const actions = Array.isArray(actionsArg) ? actionsArg : [actionsArg];
    const action = actions[0];

    const result = action(state, ...args);

    if (actions.length > 1) {
      if (isPromise(result)) {
        result.then((asyncResult) => {
          dispatch(actions.slice(1), asyncResult, ...args);
        }).catch((error) => {
          console.error('Error encountered in action promise. Action was ignored.', error, action.name);
        });
      }
      else {
        dispatch(actions.slice(1), result, ...args);
      }
    }
    else {
      if (isPromise(result) || result === null || result === undefined) {
        throw new Error(`The last function in an action must be a syncrounous pure function of state (not a Promise)! Offending action is ${action.name}.`);
      }
      updateState(result);
    }
  };

  const reset = () => updateState(initialState);

  return { getState, subscribe, reset, dispatch };
}