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JAVASCRITP XMLHttpRequest Implement Ajax notes

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Ajax

The word Ajax is no stranger to web developers, and now it's probably about the following points:

• No refresh change page data

• Asynchronous communication

$.ajax, $.get, $.post

Asynchronous Javascript and XML

•...

Ajax is an interactive Web application technology, the main purpose of the promotion of user experience, the principle is to use JavaScript XMLHttpRequest object and server communication to get data filled in the page, so as not to refresh the entire page can be feedback to the user's effect.

Commonly used Ajax
Most of the Ajax we use should be in jquery encapsulation, so we'll be relying on jquery a lot longer. And, in some usage scenarios, we only use Ajax to include the entire jquery file, which can be used to image the loading time of the page (worse when the user's network is bad).

Therefore, mastering the original Ajax writing is still very necessary, not only to get rid of jquery dependencies, but also to further deepen the understanding of asynchronous communication. It would be even better if you took the time to study the XMLHttpRequest object.

Native Ajax

• Generate XMLHttpRequest objects

The code is as follows Copy Code
var xmlreq;
if (window. XMLHttpRequest) {
XMLreq = new XMLHttpRequest ();
} else {
XMLreq = new Activatexobject (' microsoft.xmlhttp ');
}

In IE browser does not xmlhttprequest this object, to use Activatexobject (' microsoft.xmlhttp ') to replace.

• Send requests to the server

The code is as follows Copy Code

For Get method
Xmlreq.open (' Get ', ' ajax_get.html ', true);
Xmlreq.send ();

For POST method
Xmlreq.open (' POST ', ' ajax_post.html ', true);
Xmlreq.setrequestheader (' Content-type ', ' application/x-www-form-urlencoded ');
Xmlreq.send (' key=value&key2=value2 ');


The third parameter of Xmlreq.open () in the above code is to control whether the asynchronous request is to be performed, and when True is what we call asynchronous communication, which is executed in the normal JavaScript logical order when false. The purpose of true asynchrony is to not affect the normal JavaScript code execution when requesting data from the server, or it may affect the browsing of the entire page if the request time is too long or an error occurs.

• Processing server response data

The code is as follows Copy Code

Xmlreq.onreadystatechange = function () {
if (4 = xmlreq.readystate && = xmlreq.status) {
var data = Xmlreq.responsetext;
return XML data
var data = Xmlreq.responsexml;
}
}

A complete AJAX request process can be clearly understood against the Xmlreq.readystate parameter, and the different value representation process is as follows:

ReadyState process Changes
0 Request not initialized
1 server Connection established
2 Request received
3 in Request processing
4 the request is complete and the response is ready

Simple Demo
Ajax.html

The code is as follows Copy Code

    <script type= "text/javascript" charset= "UTF8"
         function My_ajax (URL, callback) {
             var xmlreq;
            if (window. XMLHttpRequest) {
                XMLreq = new XMLHttpRequest ();
           } else {
                 xmlreq = new Activatexobject (' microsoft.xmlhttp ');
           }

Xmlreq.onreadystatechange = function () {
alert (xmlreq.readystate);
if (4 = xmlreq.readystate && = xmlreq.status) {
Callback (Xmlreq.responsetext);
}
}

Xmlreq.open (' Get ', url, false);
Xmlreq.send ();
}

function Btn_click () {
My_ajax (' ajax_get.html ', function (data) {
document.getElementById (' result '). InnerHTML = data;
}
);

Alert (' OK ');
}
</script>

<body>
<input type= "button" value= "click" onclick= "Btn_click ()"/>
<div id= "Result" ></div>
</body>

Ajax_get.html

The code is as follows Copy Code

<div> I am Ajax get Data </div>

This article is intended to stimulate the time to have a look at the original things, although more complex.

Using XMLHttpRequest to achieve AJAX effects

Here we use the client through the XMLHttpRequest request server to obtain the current system time, realizes the asynchronous interaction!

Client myajax.html Code:

The code is as follows Copy Code

<title>AJAXDEMO</title>
<mce:script language= "javascript" type= "Text/javascript" ><!--
function Btn_onclick ()
{
var xmlhttp = new ActiveXObject ("Microsoft.XMLHTTP"); Creates a XMLHTTP object that is equivalent to
if (!xmlhttp) {
Alert ("Create XMLHTTP Object exception!") ");
return false;
}
XMLHTTP. Open ("Post", "Getdate1.ashx?&ts" +new Date (), false);/ready to send a POST request to the server Getdate1.ashx
Xmlhttp.onreadystatechange = function ()//need to listen for onreadystatechange events
{
if (xmlhttp.readystate = 4)//server complete
{
if (Xmlhttp.status = 200)//If the status code is 200 it is successful
{
document.getElementById ("Text1"). Value=xmlhttp.responsetext; The text returned by the ResponseText property for the server
}
Else
{
Alert ("The AJAX server returned an error!") ");
}
}
}
Xmlhttp.send (); To start sending requests
}
--></mce:script>
<body>
<input id= "Text1" type= "text" disabled= "disabled"/><input id= "button1" type= "button" value= "Show System Time" onclick= "Btn_onclick ()"/>&nbsp;
</body>


Server-side GETDATE1.ASHX code (processed with ASHX file, no HTML code required, only server-side processing of returned data)

The code is as follows Copy Code


public void ProcessRequest (HttpContext context)
{
Context. Response.ContentType = "text/html";

Context. Response.Write (DateTime.Now.ToString ()); Show service-side time
}

This article is an English version of an article which is originally in the Chinese language on aliyun.com and is provided for information purposes only. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. If you have any concerns or complaints relating to the article, please send an email, providing a detailed description of the concern or complaint, to info-contact@alibabacloud.com. A staff member will contact you within 5 working days. Once verified, infringing content will be removed immediately.

Related Keywords:
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