The principle of small white learning ajax-02-

Basic principle

The principle is simple.

1. New XHR
2. Xhr.onreadystatechange
3. Xhr.open (method, URL, async)
4. Xhr.send ()

Create a Xhr object

Compatible with the IE6, refer to Masaki greatly written:

var xhr = new (window. xmlhttprequest| | ActiveXObject) (' Microsoft.XMLHTTP ')

XHR Create request

Xhr.open (method, URL, async) is a create request and receives three parameters:

1. The type of sending request, mainly "GET" and "POST";
2. The requested URL, if the Get,data parameter is stitched behind the URL,
   How to Post,xhr.send (data), and set the header;

3. Async is async, default is true to indicate async, and false for synchronization.

XHR Response Request

The Onreadychange object has a readystate attribute with a value of 5

0: not initialized. The open () method has not been called

1: Start. The open () method has been called, but the Send () method has not been called

2: Send. The Send () method has been called, but the response has not been received

3: Receive. Part of the response data has been accepted

4: Complete. All response data has been accepted and can be used on the client

Xhr.onreadystatechange = function() {  if (xhr.readystate = = = 4) {      var status = xhr.status;      if (Status >= & Status < | | status = = = 304) {          console.log (xhr.responsetext)  }}}  

Send Request

Xhr.send (data), the format of data is ' param1=value1&param2=value2 ';

It is important to note that when the type is post, the setRequestHeader is placed after Xhr.open ().

The principle of small white learning ajax-02-