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- # _createReduce.js

- ¶

      import isArrayLike from './_isArrayLike.js';
      import keys from './keys.js';
      import optimizeCb from './_optimizeCb.js';

- ¶

  Internal helper to create a reducing function, iterating left or right.

      export default function createReduce(dir) {

- ¶

  Wrap code that reassigns argument variables in a separate function than the one that accesses `arguments.length` to avoid a perf hit. (#1991)

        var reducer = function(obj, iteratee, memo, initial) {
          var _keys = !isArrayLike(obj) && keys(obj),
              length = (_keys || obj).length,
              index = dir > 0 ? 0 : length - 1;
          if (!initial) {
            memo = obj[_keys ? _keys[index] : index];
            index += dir;
          }
          for (; index >= 0 && index < length; index += dir) {
            var currentKey = _keys ? _keys[index] : index;
            memo = iteratee(memo, obj[currentKey], currentKey, obj);
          }
          return memo;
        };

        return function(obj, iteratee, memo, context) {
          var initial = arguments.length >= 3;
          return reducer(obj, optimizeCb(iteratee, context, 4), memo, initial);
        };
      }