Bump to v4.0.0.

internal/baseSum.js

@@ -1,19 +1,27 @@
-define(['./baseEach'], function(baseEach) {
+define([], function() {
+
+  /** Used as a safe reference for `undefined` in pre-ES5 environments. */
+  var undefined;
 
   /**
-   * The base implementation of `_.sum` without support for callback shorthands
-   * and `this` binding.
+   * The base implementation of `_.sum` without support for iteratee shorthands.
    *
    * @private
-   * @param {Array|Object|string} collection The collection to iterate over.
+   * @param {Array} array The array to iterate over.
    * @param {Function} iteratee The function invoked per iteration.
    * @returns {number} Returns the sum.
    */
-  function baseSum(collection, iteratee) {
-    var result = 0;
-    baseEach(collection, function(value, index, collection) {
-      result += +iteratee(value, index, collection) || 0;
-    });
+  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;
   }