Add npm-package

npm-package/_baseIsSet.js

@@ -0,0 +1,18 @@
+var getTag = require('./_getTag'),
+    isObjectLike = require('./isObjectLike');
+
+/** `Object#toString` result references. */
+var setTag = '[object Set]';
+
+/**
+ * The base implementation of `_.isSet` without Node.js optimizations.
+ *
+ * @private
+ * @param {*} value The value to check.
+ * @returns {boolean} Returns `true` if `value` is a set, else `false`.
+ */
+function baseIsSet(value) {
+  return isObjectLike(value) && getTag(value) == setTag;
+}
+
+module.exports = baseIsSet;