Function combineReducers

code/redux/public/app.js:21308–21369

* 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

(reducers)

 * passed object, and builds a state object with the same shape.
 */
function combineReducers(reducers) {
  var reducerKeys = Object.keys(reducers);
  var finalReducers = {};
  for (var i = 0; i < reducerKeys.length; i++) {
    var key = reducerKeys[i];

    if (process.env.NODE_ENV !== 'production') {
      if (typeof reducers[key] === 'undefined') {
        (0, _warning2['default'])('No reducer provided for key "' + key + '"');
      }
    }

    if (typeof reducers[key] === 'function') {
      finalReducers[key] = reducers[key];
    }
  }
  var finalReducerKeys = Object.keys(finalReducers);

  var unexpectedKeyCache = void 0;
  if (process.env.NODE_ENV !== 'production') {
    unexpectedKeyCache = {};
  }

  var shapeAssertionError = void 0;
  try {
    assertReducerShape(finalReducers);
  } catch (e) {
    shapeAssertionError = e;
  }

  return function combination() {
    var state = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : {};
    var action = arguments[1];

    if (shapeAssertionError) {
      throw shapeAssertionError;
    }

    if (process.env.NODE_ENV !== 'production') {
      var warningMessage = getUnexpectedStateShapeWarningMessage(state, finalReducers, action, unexpectedKeyCache);
      if (warningMessage) {
        (0, _warning2['default'])(warningMessage);
      }
    }

    var hasChanged = false;
    var nextState = {};
    for (var _i = 0; _i < finalReducerKeys.length; _i++) {
      var _key = finalReducerKeys[_i];
      var reducer = finalReducers[_key];
      var previousStateForKey = state[_key];
      var nextStateForKey = reducer(previousStateForKey, action);
      if (typeof nextStateForKey === 'undefined') {
        var errorMessage = getUndefinedStateErrorMessage(_key, action);
        throw new Error(errorMessage);
      }
      nextState[_key] = nextStateForKey;
      hasChanged = hasChanged || nextStateForKey !== previousStateForKey;