Add WeakSet example

Author: tshemsedinov

JavaScript/5-weak.js

@@ -0,0 +1,36 @@
+'use strict';
+
+const cities = new Set([
+  { name: 'Beijing' },
+  { name: 'Kiev' },
+  { name: 'London' },
+  { name: 'Baghdad' }
+]);
+
+const list = new WeakSet();
+for (const city of cities) {
+  console.log('Add city', city, 'to WeakSet');
+  list.add(city);
+}
+
+console.dir({ cities, list });
+
+const iterator = cities.values();
+
+const beijing = iterator.next().value;
+console.log('select', beijing);
+
+iterator.next();
+
+const london = iterator.next().value;
+console.log('select', london);
+
+cities.delete(london);
+console.log('remove', london, 'from Set');
+
+list.delete(beijing);
+console.log('remove', beijing, 'from WeakSet');
+
+for (const city of cities) {
+  console.log('City', city, 'in WeakSet', list.has(city));
+}