--- /dev/null
+'use strict';
+var $ = require('../internals/export');
+var IS_PURE = require('../internals/is-pure');
+var $upsert = require('../internals/map-upsert');
+
+// `WeakMap.prototype.upsert` method
+// https://github.com/thumbsupep/proposal-upsert
+$({ target: 'WeakMap', proto: true, real: true, forced: IS_PURE }, {
+ upsert: $upsert
+});