Express addition

node_modules/core-js/library/modules/es6.weak-set.js

@@ -0,0 +1,14 @@
+'use strict';
+var weak = require('./_collection-weak');
+var validate = require('./_validate-collection');
+var WEAK_SET = 'WeakSet';
+
+// 23.4 WeakSet Objects
+require('./_collection')(WEAK_SET, function (get) {
+  return function WeakSet() { return get(this, arguments.length > 0 ? arguments[0] : undefined); };
+}, {
+  // 23.4.3.1 WeakSet.prototype.add(value)
+  add: function add(value) {
+    return weak.def(validate(this, WEAK_SET), value, true);
+  }
+}, weak, false, true);