What is the best online course for learning AJAX?

You can get lots of Ajax Courses free from you searched for ajax by googling sites like: https://www.udacity.com/course/intro-to-ajax--ud110

Or learn AJAX with PHP from Scratch using jQuery. 

Or Ajax and jQuery beginners tutorials - YouTube *channel 

Basm allah alrahman alrahim

I think Udemy website has a lot of AJAX courses

Yasmeen, I'm a fan of Brad Traversy of Traversy Media. He is basically a php line of developer. He explain things nicely and practically that makes us understand with practical experience. Here is a link on AJAX:https://www.youtube.com/watch?v=82hnvUYY6QABy the way I can explain you ajax, you can contact me by whatsapp or email.Thanks