function baseReduce(collection, iteratee, accumulator, initAccum, eachFunc) {
    eachFunc(collection, function(value, index, collection) {
      accumulator = initAccum
        ? (initAccum = false, value)
        : iteratee(accumulator, value, index, collection);
    });
    return accumulator;
  }
The base implementation of `_.reduce` and `_.reduceRight`, without support
for iteratee shorthands, which iterates over `collection` using `eachFunc`.

@private
@param {Array|Object} collection The collection to iterate over.
@param {Function} iteratee The function invoked per iteration.
@param {*} accumulator The initial value.
@param {boolean} initAccum Specify using the first or last element of
 `collection` as the initial value.
@param {Function} eachFunc The function to iterate over `collection`.
@returns {*} Returns the accumulated value.