--- /dev/null
+/**
+ * The base implementation of `_.sum` and `_.sumBy` without support for
+ * iteratee shorthands.
+ *
+ * @private
+ * @param {Array} array The array to iterate over.
+ * @param {Function} iteratee The function invoked per iteration.
+ * @returns {number} Returns the sum.
+ */
+function baseSum(array, iteratee) {
+ var result,
+ index = -1,
+ length = array.length;
+
+ while (++index < length) {
+ var current = iteratee(array[index]);
+ if (current !== undefined) {
+ result = result === undefined ? current : (result + current);
+ }
+ }
+ return result;
+}
+
+module.exports = baseSum;