JavaScript object-oriented encapsulation of XMLHttpRequest asynchronous requests

function CallBackObject()
{
this.XmlHttp = this.GetHttpObject();
}
CallBackObject.prototype.GetHttpObject = function() //动态为CallBackObject的原型添加了GetHttpObject共有方法
{
//第一步：创建XMLHttpRequest对象
//进行兼容性判断
var xmlhttp;
/*@cc_on
@if (@_jscript_version >= 5)
try {
xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
} catch (E) {
xmlhttp = false;
}
}
@else
xmlhttp = false;
@end @*/
if (!xmlhttp && typeof XMLHttpRequest != 'undefined') {
try {
xmlhttp = new XMLHttpRequest();
} catch (e) {
xmlhttp = false;
}
}
return xmlhttp;
}
CallBackObject.prototype.DoCallBack = function(URL)
{
if( this.XmlHttp )
{
if( this.XmlHttp.readyState == 4 || this.XmlHttp.readyState == 0 )
{
var oThis = this;
//第二步：注册回调方法，当服务器处理结束返回数据以后利用回调方法实现局部的页面刷新数据
//这个回调方法实际上在每次XMLHttpRequest对象的readyState属性的值发生变化的时候都会被调用
this.XmlHttp.onreadystatechange = function() {
//根据XmlHttp.readyState返回值不同调用不同的方法。
oThis.ReadyStateChange();
};
//第三步：设置和服务器交互的相应参数
this.XmlHttp.open('POST', URL);
this.XmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
//第四步：设置向服务器发送的数据，启动和服务器端交互
this.XmlHttp.send(null);
}
}
}
CallBackObject.prototype.AbortCallBack = function()
{
if( this.XmlHttp )
this.XmlHttp.abort();
}
CallBackObject.prototype.ReadyStateChange = function() {
//第五步：判断和服务器交互是否完成，还要判断服务器端是否正确返回数据
//this.XmlHttp.readyState == 0初始化状态。XMLHttpRequest 对象已创建或已被 abort() 方法重置。
if (this.XmlHttp.readyState == 1) {
//open() 方法已调用，但是 send() 方法未调用。请求还没有被发送。
this.OnLoading();
}
else if (this.XmlHttp.readyState == 2) {
//Send() 方法已调用，HTTP 请求已发送到 Web 服务器。未接收到响应。
this.OnLoaded();
}
else if (this.XmlHttp.readyState == 3) {
//Receiving 所有响应头部都已经接收到。响应体开始接收但未完成。
this.OnInteractive();
}
else if (this.XmlHttp.readyState == 4) {
//Loaded HTTP 响应已经完全接收。
if (this.XmlHttp.status == 0)
this.OnAbort();
else if (this.XmlHttp.status == 200 && this.XmlHttp.statusText == "OK")
this.OnComplete(this.XmlHttp.responseText, this.XmlHttp.responseXML);
else
this.OnError(this.XmlHttp.status, this.XmlHttp.statusText, this.XmlHttp.responseText);
}
}
CallBackObject.prototype.OnLoading = function()
{
// Loading
}
CallBackObject.prototype.OnLoaded = function()
{
// Loaded
}
CallBackObject.prototype.OnInteractive = function()
{
// Interactive
}
CallBackObject.prototype.OnComplete = function(responseText, responseXml)
{
// Complete
}
CallBackObject.prototype.OnAbort = function()
{
// Abort
}
CallBackObject.prototype.OnError = function(status, statusText)
{
// Error
}

The calling method is as follows:

<script type="text/javascript">
function createRequest()
{
var name = escape(document.getElementById("name").value);
var cbo = new CallBackObject();
cbo.OnComplete = Cbo_Complete;
cbo.onError = Cbo_Error;
cbo.OnLoaded = OnLoading;
cbo.DoCallBack("AjaxTest.aspx?name=" + name);
}

function OnLoading() {
alert("OnLoading " );
}

function Cbo_Complete(responseText, responseXML)
{
alert("成功 "+responseText);
}

function Cbo_Error(status, statusText, responseText)
{
alert(responseText);
}
</script>

onreadystatechange event
Whenever the readyState value changes, the XMLHttpRequest object will fire a readystatechange event. Among them, the onreadystatechange attribute receives an EventListener value - indicating to the method that the object will be activated whenever the readyState value changes.
　responseText attribute
This responseText attribute contains the text content of the HTTP response received by the client. When the readyState value is 0, 1, or 2, responseText contains an empty string. When the readyState value is 3 (receiving), the response contains the client's unfinished response information. When readyState is 4 (loaded), the responseText contains complete response information.
ResponseXML attribute
This responseXML attribute is used to describe the XML response when a complete HTTP response is received (readyState is 4); at this time, the Content-Type header specifies the MIME (media) type as text/xml, application /xml or ending with +xml. If the Content-Type header does not contain one of these media types, the value of responseXML is null. Whenever the readyState value is not 4, the value of the responseXML is also null.
In fact, the responseXML attribute value is an object of document interface type, used to describe the document being analyzed. If the document cannot be parsed (for example, if the document is not well-formed or the document's corresponding character encoding is not supported), then the value of responseXML will be null.
Status attribute
This status attribute describes the HTTP status code, and its type is short. Moreover, this status attribute is only available when the readyState value is 3 (receiving) or 4 (loaded). Attempting to access the status value when readyState is less than 3 will throw an exception.
StatusText attribute
This statusText attribute describes the HTTP status code text; and is only available when the readyState value is 3 or 4. Attempting to access the statusText property when readyState is any other value will throw an exception.

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