js file:
1. Accept data, split and splicing processing
2.var xhr = XMLHTTPRequest（）
3. Determine the request type, get or post; there are parameters in the url of get, but not in the post (can not be directly seen by the user); write xhr.open(); Write xhr.setRequestHeader().
4. Judging that the readystate has changed to 4, indicating that the request data is over; if it is judged that it is successfully returned (200), the output //The idea of detecting readystate here is asynchronous.
Handwritten stickers:
