Fix typing for main script. Add jsdom for tests

Author: LLIu33

README.MD

@@ -19,4 +19,9 @@ var allElements = mapElement(htmlNode, "//html[1]", {
     "//html[1]" : html
 });
 console.log(allElements);
+```
+
+## Test 
+```sh
+npm run test
 ```