redux/lib/combineReducers.js

Predictable state container for JavaScript apps

'use strict';

exports.__esModule = true;
exports['default'] = combineReducers;

function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { 'default': obj }; }

var _createStore = require('./createStore');

var _utilsIsPlainObject = require('./utils/isPlainObject');

var _utilsIsPlainObject2 = _interopRequireDefault(_utilsIsPlainObject);

var _utilsMapValues = require('./utils/mapValues');

var _utilsMapValues2 = _interopRequireDefault(_utilsMapValues);

var _utilsPick = require('./utils/pick');

var _utilsPick2 = _interopRequireDefault(_utilsPick);

/* eslint-disable no-console */

function getUndefinedStateErrorMessage(key, action) {
  var actionType = action && action.type;
  var actionName = actionType && '"' + actionType.toString() + '"' || 'an action';

  return 'Reducer "' + key + '" returned undefined handling ' + actionName + '. ' + 'To ignore an action, you must explicitly return the previous state.';
}

function getUnexpectedStateShapeWarningMessage(inputState, reducers, action) {
  var reducerKeys = Object.keys(reducers);
  var argumentName = action && action.type === _createStore.ActionTypes.INIT ? 'initialState argument passed to createStore' : 'previous state received by the reducer';

  if (reducerKeys.length === 0) {
    return 'Store does not have a valid reducer. Make sure the argument passed ' + 'to combineReducers is an object whose values are reducers.';
  }

  if (!_utilsIsPlainObject2['default'](inputState)) {
    return 'The ' + argumentName + ' has unexpected type of "' + ({}).toString.call(inputState).match(/\s([a-z|A-Z]+)/)[1] + '". Expected argument to be an object with the following ' + ('keys: "' + reducerKeys.join('", "') + '"');
  }

  var unexpectedKeys = Object.keys(inputState).filter(function (key) {
    return !reducers.hasOwnProperty(key);
  });

  if (unexpectedKeys.length > 0) {
    return 'Unexpected ' + (unexpectedKeys.length > 1 ? 'keys' : 'key') + ' ' + ('"' + unexpectedKeys.join('", "') + '" found in ' + argumentName + '. ') + 'Expected to find one of the known reducer keys instead: ' + ('"' + reducerKeys.join('", "') + '". Unexpected keys will be ignored.');
  }
}

function assertReducerSanity(reducers) {
  Object.keys(reducers).forEach(function (key) {
    var reducer = reducers[key];
    var initialState = reducer(undefined, { type: _createStore.ActionTypes.INIT });

    if (typeof initialState === 'undefined') {
      throw new Error('Reducer "' + key + '" returned undefined during initialization. ' + 'If the state passed to the reducer is undefined, you must ' + 'explicitly return the initial state. The initial state may ' + 'not be undefined.');
    }

    var type = '@@redux/PROBE_UNKNOWN_ACTION_' + Math.random().toString(36).substring(7).split('').join('.');
    if (typeof reducer(undefined, { type: type }) === 'undefined') {
      throw new Error('Reducer "' + key + '" returned undefined when probed with a random type. ' + ('Don\'t try to handle ' + _createStore.ActionTypes.INIT + ' or other actions in "redux/*" ') + 'namespace. They are considered private. Instead, you must return the ' + 'current state for any unknown actions, unless it is undefined, ' + 'in which case you must return the initial state, regardless of the ' + 'action type. The initial state may not be undefined.');
    }
  });
}

/**
 * Turns an object whose values are different reducer functions, into a single
 * reducer function. It will call every child reducer, and gather their results
 * into a single state object, whose keys correspond to the keys of the passed
 * reducer functions.
 *
 * @param {Object} reducers An object whose values correspond to different
 * reducer functions that need to be combined into one. One handy way to obtain
 * it is to use ES6 `import * as reducers` syntax. The reducers may never return
 * undefined for any action. Instead, they should return their initial state
 * if the state passed to them was undefined, and the current state for any
 * unrecognized action.
 *
 * @returns {Function} A reducer function that invokes every reducer inside the
 * passed object, and builds a state object with the same shape.
 */

function combineReducers(reducers) {
  var finalReducers = _utilsPick2['default'](reducers, function (val) {
    return typeof val === 'function';
  });
  var sanityError;

  try {
    assertReducerSanity(finalReducers);
  } catch (e) {
    sanityError = e;
  }

  return function combination(state, action) {
    if (state === undefined) state = {};

    if (sanityError) {
      throw sanityError;
    }

    if (process.env.NODE_ENV !== 'production') {
      var warningMessage = getUnexpectedStateShapeWarningMessage(state, finalReducers, action);
      if (warningMessage) {
        console.error(warningMessage);
      }
    }

    var hasChanged = false;
    var finalState = _utilsMapValues2['default'](finalReducers, function (reducer, key) {
      var previousStateForKey = state[key];
      var nextStateForKey = reducer(previousStateForKey, action);
      if (typeof nextStateForKey === 'undefined') {
        var errorMessage = getUndefinedStateErrorMessage(key, action);
        throw new Error(errorMessage);
      }
      hasChanged = hasChanged || nextStateForKey !== previousStateForKey;
      return nextStateForKey;
    });

    return hasChanged ? finalState : state;
  };
}

module.exports = exports['default'];