Congratulations on completing this course! We have come a long way since the beginning, so let's recap:
In part 1, you learned about the DOM — how to get access to specific elements or groups of elements; how to navigate from one element to another; how to add, modify and remove elements; and how to listen for and react to DOM events.
In part 2, you learned about forms — how to hook up various input types and extract their value; how to handle form submission; several strategies for validating user input, and you made your first AJAX GET request.
In part 3, you dove deeper into AJAX — you learned about various strategies for dealing with asynchronous code; you made your first POST request; you learned how to leverage async/await to chain multiple requests together, both in parallel and in series; and you learned about error handling and the mentality that goes with it.
Wow, that's a lot! Well done for sticking with it all the way to the end!