problems(js): add “2618. Check if Object Instance of Class”

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/js/check-if-object-instance-of-class.js

@@ -0,0 +1,16 @@
+/**
+ * @param {any} obj
+ * @param {any} classFunction
+ * @return {boolean}
+ */
+var checkIfInstanceOf = function(obj, classFunction) {
+    if (obj === null || obj === undefined || typeof classFunction !== "function") {
+        return false;
+    }
+
+    return Object(obj) instanceof classFunction;
+};
+
+/**
+ * checkIfInstanceOf(new Date(), Date); // true
+ */