Babel 5 vs Babel 6 Difference

0.md

Babel 5 will incorrectly allow a let declration shadow an outter var declaration. See below and note the user of var _filters on line 7 by Babel 6 instead of var filters by Babel 5 (which shadows the var filters declared on line 2).

1-es6.js

export default (filters = {}, action = {}) => {
  switch (action.type) {
    case UPDATE_FILTERS:
      let filters = {...filters}
      filters[action.filter] = action.value
  }

  // Return the new state.
  return filters
}

2-es5-babel5.js

exports['default'] = function () {
  var filters = arguments.length <= 0 || arguments[0] === undefined ? {} : arguments[0];
  var action = arguments.length <= 1 || arguments[1] === undefined ? {} : arguments[1];

  switch (action.type) {
    case _actions.UPDATE_FILTERS:
      var filters = _extends({}, filters);
      filters[action.filter] = action.value;
  }

  // Return the new state.
  return filters;
};

3-es5-babel6.js

exports.default = function () {
  var filters = arguments.length <= 0 || arguments[0] === undefined ? {} : arguments[0];
  var action = arguments.length <= 1 || arguments[1] === undefined ? {} : arguments[1];

  switch (action.type) {
    case _actions.UPDATE_FILTERS:
      var _filters = _extends({}, _filters);
      _filters[action.filter] = action.value;
  }

  // Return the new state.
  return filters;
};