Ajax Real-time verification of user name/mailbox and other existing code package _ php instance

A website uses Ajax technology, which not only improves the user experience of the website, but also greatly saves valuable bandwidth and reduces the server load (instead of interacting with the entire webpage content, but is partial ). Today, we will share an example of "using Ajax technology to check whether a user name exists.
The principle flowchart of using Ajax technology to check whether a user name exists:

Final result:

The code is as follows:

Ajax detection username