Move internal modules to “internal” folder.

.internal/baseMap.js

@@ -0,0 +1,22 @@
+import baseEach from './.internal/baseEach.js';
+import isArrayLike from './isArrayLike.js';
+
+/**
+ * The base implementation of `map`.
+ *
+ * @private
+ * @param {Array|Object} collection The collection to iterate over.
+ * @param {Function} iteratee The function invoked per iteration.
+ * @returns {Array} Returns the new mapped array.
+ */
+function baseMap(collection, iteratee) {
+  let index = -1;
+  const result = isArrayLike(collection) ? Array(collection.length) : [];
+
+  baseEach(collection, (value, key, collection) => {
+    result[++index] = iteratee(value, key, collection);
+  });
+  return result;
+}
+
+export default baseMap;