index.js

/* globals define */
(function (root, factory) {
  "use strict";
  if (typeof define === "function" && define.amd) {
    define([], factory);
  } else if (typeof exports === "object") {
    module.exports = factory();
  } else {
    root.atom = factory();
  }
})(this, function () {
  "use strict";

  return function (reducers, initialState) {
    if (typeof reducers === "function") {
      reducers = [reducers];
    }
    var listeners = [];
    var state = initialState;

    reducers.push(function setStateReducer(action, state) {
      return action && action.type === "__ATOM_SET_STATE__"
        ? Object.assign(state, action.payload)
        : state;
    });

    return {
      addReducer: addReducer,
      removeReducer: removeReducer,
      dispatch: dispatch,
      subscribe: subscribe,
      unsubscribe: unsubscribe,
      getState: getState,
      setState: setState,
    };

    function addReducer(reducer) {
      if (typeof reducer !== "function") {
        throw new E("reducer must be a function");
      }
      reducers.push(reducer);
    }

    function removeReducer(reducer) {
      if (!reducer) return;
      const idx = reducers.findIndex((l) => l === reducer);
      idx > -1 && reducers.splice(idx, 1);
    }

    function dispatch(/* action[, action1, action2, ...] */) {
      var len = arguments.length;
      var newState = getState();
      for (var x = 0; x < len; x++) {
        newState = callReducers(reducers, arguments[x], newState);
      }
      if (validState(newState)) {
        cb(newState);
      }
    }

    function subscribe(listener) {
      if (typeof listener !== "function") {
        throw new E("listener must be a function");
      }
      listeners.push(listener);
      return function () {
        unsubscribe(listener);
      };
    }

    function unsubscribe(listener) {
      if (!listener) return;
      const idx = listeners.findIndex((l) => l === listener);
      idx > -1 && listeners.splice(idx, 1);
    }

    function getState() {
      return typeof state === "object" ? Object.assign({}, state) : state;
    }

    function setState(newState, meta) {
      dispatch({ type: "__ATOM_SET_STATE__", payload: newState, meta: meta });
    }

    // Private

    function callReducers(fns, action, state) {
      var newState = state;
      var len = reducers.length;
      var ret;
      for (var x = 0; x < len; x++) {
        ret = fns[x](action, newState);
        if (validState(ret)) {
          newState = ret;
        }
      }
      return newState;
    }

    function cb(newState) {
      state = newState;
      for (var x = 0; x < listeners.length; x++) {
        listeners[x]();
      }
    }

    function validState(newState) {
      if (newState === undefined) {
        throw new E("Reducer must return a value.");
      } else if (typeof newState.then === "function") {
        throw new E("Reducer cannot return a Promise.");
      } else if (typeof newState === "function") {
        newState(dispatch);
      } else {
        return true;
      }
    }

    function E(message) {
      this.message = message;
      this.name = "AtomException";
      this.toString = function () {
        return this.name + ": " + this.message;
      };
    }
  };
});