Modularize master branch.

size.js

@@ -0,0 +1,46 @@
+import baseKeys from './_baseKeys.js';
+import getTag from './_getTag.js';
+import isArrayLike from './isArrayLike.js';
+import isString from './isString.js';
+import stringSize from './_stringSize.js';
+
+/** `Object#toString` result references. */
+var mapTag = '[object Map]',
+    setTag = '[object Set]';
+
+/**
+ * Gets the size of `collection` by returning its length for array-like
+ * values or the number of own enumerable string keyed properties for objects.
+ *
+ * @static
+ * @memberOf _
+ * @since 0.1.0
+ * @category Collection
+ * @param {Array|Object|string} collection The collection to inspect.
+ * @returns {number} Returns the collection size.
+ * @example
+ *
+ * _.size([1, 2, 3]);
+ * // => 3
+ *
+ * _.size({ 'a': 1, 'b': 2 });
+ * // => 2
+ *
+ * _.size('pebbles');
+ * // => 7
+ */
+function size(collection) {
+  if (collection == null) {
+    return 0;
+  }
+  if (isArrayLike(collection)) {
+    return isString(collection) ? stringSize(collection) : collection.length;
+  }
+  var tag = getTag(collection);
+  if (tag == mapTag || tag == setTag) {
+    return collection.size;
+  }
+  return baseKeys(collection).length;
+}
+
+export default size;