Bump to v4.0.0.

mergeWith.js

@@ -0,0 +1,43 @@
+import baseMerge from './internal/baseMerge';
+import createAssigner from './internal/createAssigner';
+
+/**
+ * This method is like `_.merge` except that it accepts `customizer` which
+ * is invoked to produce the merged values of the destination and source
+ * properties. If `customizer` returns `undefined` merging is handled by the
+ * method instead. The `customizer` is invoked with seven arguments:
+ * (objValue, srcValue, key, object, source, stack).
+ *
+ * @static
+ * @memberOf _
+ * @category Object
+ * @param {Object} object The destination object.
+ * @param {...Object} sources The source objects.
+ * @param {Function} customizer The function to customize assigned values.
+ * @returns {Object} Returns `object`.
+ * @example
+ *
+ * function customizer(objValue, srcValue) {
+ *   if (_.isArray(objValue)) {
+ *     return objValue.concat(srcValue);
+ *   }
+ * }
+ *
+ * var object = {
+ *   'fruits': ['apple'],
+ *   'vegetables': ['beet']
+ * };
+ *
+ * var other = {
+ *   'fruits': ['banana'],
+ *   'vegetables': ['carrot']
+ * };
+ *
+ * _.mergeWith(object, other, customizer);
+ * // => { 'fruits': ['apple', 'banana'], 'vegetables': ['beet', 'carrot'] }
+ */
+var mergeWith = createAssigner(function(object, source, customizer) {
+  baseMerge(object, source, customizer);
+});
+
+export default mergeWith;