Ajax Full Name
Asynchronous JavaScript and XML (asynchronous JavaScript and XML)
Synchronous and asynchronous
An asynchronous transmission is a character-oriented transmission in which the unit is a character
Synchronous transmission is a bit-oriented, unit is a frame, transmission requires the receiver and the sender's clock is consistent.
Understanding Ajax through XMLHttpRequest
The AJAX principle is simply to send an asynchronous request to the server via XMLHttpRequest, get the data from the server, and then use JavaScript to manipulate the DOM and refresh the page.
XMLHttpRequest Object Properties
! [XMLHttpRequest Object Properties] (Http://7u2eqw.com1.z0.glb.clouddn.com/XMLHTTPRequest object properties. png)
Ajax is the use of JavaScript technology and XMLHttpRequest objects between Web Forms and servers, when the user requests to the server, the data sent to the JavaScript code instead of directly to the server, JavaScript code in the background to send an asynchronous request, The server then returns the data to the JavaScript code. After the JavaScript code receives the data, manipulate the DOM to update the page data.
Ajax Synchronous and asynchronous
Async: Ajax is always executed without blocking the response from the server, so it is not effective to assign values to variables in a function when using asynchronous Ajax.
Synchronization: Ajax is blocking, waiting for the server to return data to perform the next step.
AJAX schematic diagram
Summary of Ajax Principles