Added a few type checking snippets from lodash

snippets/isWeakSet.md

@@ -0,0 +1,13 @@
+### isWeakSet
+
+Checks if value is classified as a WeakSet object.
+
+Use the `instanceof`operator to check if the provided value is a `WeakSet` object.
+
+```js
+const isWeakSet = val => val instanceof WeakSet;
+```
+
+```js
+isWeakSet(new WeakSet()); // true
+```