JQuery Ajax函数使用相同的数据调用两次

I'm building a very simple page that is a to-do list. It accepts input from a user via a form for new to-dos, POSTs the to-do to the server, then receives (almost) the same data back and adds it to a list. However, every time data is supposed to be sent to the server, the $.ajax function is called twice.I'm building a very simple page that is a to-do