AJAX principle:
What is ajax : Ajax is A synchronous J avascript A nd X ML (asynchronous JavaScript and XML
Asynchronous: multiple things can be done at once
Synchronous: Only one action (instruction) can be executed at a time
js is a synchronous language with single-threaded blocking loading. Because it is single-threaded, it is blocking loading, so it can only be a synchronous language.
ajax is simulated asynchronous
A data format of xml, which was gradually eliminated because of the complicated writing method, now uses the json format
requested tool
What is a server : In the process of surfing the Internet, the computer responsible for storing and providing resources to the outside world is called a server.
What is url : Uniform resource locator in Chinese, which is used to identify the storage location of each resource on the Internet. Only through the URL address can the browser correctly locate the storage location of the resource and successfully access the corresponding resource
Common URL example: www.baidu.com
The URL address generally consists of three parts: the communication protocol between the client and the server
The name of the server where the resource is stored , and the specific storage location of the resource on the server
