Introduction to the relationship of Ajax four elements _ajax related

Using JavaScript to manipulate DOM elements to refresh pages and reorganize data, rely on CSS to provide a consistent interface for applications, use XMLHttpRequest objects to communicate asynchronously with servers, submit requests in the background, and get the most recent data. JavaScript defines business rules and processes in which applications get data from the server in the background through XMLHttpRequest objects, changing the appearance of the interface through CSS and DOM.

Attention:
1, Ajax is not just JavaScript, but a group of technology combination
2, XMLHttpRequest and server communication to obtain data is a background asynchronous way