Modularize master branch.

_getTag.js

@@ -0,0 +1,58 @@
+import DataView from './_DataView.js';
+import Map from './_Map.js';
+import Promise from './_Promise.js';
+import Set from './_Set.js';
+import WeakMap from './_WeakMap.js';
+import baseGetTag from './_baseGetTag.js';
+import toSource from './_toSource.js';
+
+/** `Object#toString` result references. */
+var mapTag = '[object Map]',
+    objectTag = '[object Object]',
+    promiseTag = '[object Promise]',
+    setTag = '[object Set]',
+    weakMapTag = '[object WeakMap]';
+
+var dataViewTag = '[object DataView]';
+
+/** Used to detect maps, sets, and weakmaps. */
+var dataViewCtorString = toSource(DataView),
+    mapCtorString = toSource(Map),
+    promiseCtorString = toSource(Promise),
+    setCtorString = toSource(Set),
+    weakMapCtorString = toSource(WeakMap);
+
+/**
+ * Gets the `toStringTag` of `value`.
+ *
+ * @private
+ * @param {*} value The value to query.
+ * @returns {string} Returns the `toStringTag`.
+ */
+var getTag = baseGetTag;
+
+// Fallback for data views, maps, sets, and weak maps in IE 11 and promises in Node.js < 6.
+if ((DataView && getTag(new DataView(new ArrayBuffer(1))) != dataViewTag) ||
+    (Map && getTag(new Map) != mapTag) ||
+    (Promise && getTag(Promise.resolve()) != promiseTag) ||
+    (Set && getTag(new Set) != setTag) ||
+    (WeakMap && getTag(new WeakMap) != weakMapTag)) {
+  getTag = function(value) {
+    var result = baseGetTag(value),
+        Ctor = result == objectTag ? value.constructor : undefined,
+        ctorString = Ctor ? toSource(Ctor) : '';
+
+    if (ctorString) {
+      switch (ctorString) {
+        case dataViewCtorString: return dataViewTag;
+        case mapCtorString: return mapTag;
+        case promiseCtorString: return promiseTag;
+        case setCtorString: return setTag;
+        case weakMapCtorString: return weakMapTag;
+      }
+    }
+    return result;
+  };
+}
+
+export default getTag;