Implementing AJAX asynchronous requests

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Implementing Ajax

Ajax:

Asynchronous: Asynchronous

Javascript

And: And

Xml

Ajax technology is the ability to use JavaScript and XML to implement asynchronous interactions

Ajax has its own engine, and the traditional interaction is that the client interacts directly with the sever,

Ajax is the client sends the request to the Ajax engine, and the Ajax engine sends the request to the server,

This implements the asynchronous request

1. Creating an Ajax Object

function createxhr () {    try{returnnew XMLHttpRequest ()}catch(e) {}                      //W3C, also supported    in IE High version Try {returnnew activexobject (' Microsoft.XMLHTTP ')} Catch (e) {}   //ie    alert (' Please change browser ');}

2. Initializing Ajax objects

Xhr.open (' Get ', ' demo01.php ');//open (Mehod,url)

You can also set the request header information here

setRequestHeader (Header,value)///can use 1 (' if-modified-since ', ' 0 ') to eliminate the cache, or you can use the plus random number 2 math.random ()

or random time 3 var url= ' demo01.php?name=huohaifeng&_= ' + new Date (). GetTime ();

or 4 Set the header ("Cache-control:no-cache") on the server side;

3. Send Request

Send (content) only sends the request when the Send method is called, content:post the data that is passed when the request is requested, and if the GET request writes NULL directly

4. Execute callback function

Onreadystatechange=funtion () {} triggers when the Ajax object status code changes

Some other Ajax properties:

Readystate:ajax Object Status Code: 0-4

0: Indicates that the object is established but not initialized

1: Indicates that the object has been initialized but not sent

2: The Send method has been called for request

3: Receiving data

4: Receive complete

Status

The HTTP response status code received by the Ajax object, such as: 200 302 304 404

StatusText

The HTTP response status text received by the Ajax object such as: OK, not found

Reponsetext

The Ajax object receives the HTTP response body string (text/html)

Responsexml

HTTP response body content received by the Ajax object (Text/xml)

Implementing AJAX asynchronous requests