创建Ajax

//创建XHR对象的构造函数
function creatXHR (){
if ( typeOf XMLHttpRequest != “undefined”){
return new XMLHttpRequest ();
} else if （typeOf ActiveXObject != “undefined”）
 {
  if(typeOf arguments.callee.activeXString != “string” ){
var version = [ “MSXML2.XMLHttp.6.0”, “MSXML2.XMLHttp.3.0” , “MSXML2.XMLHttp”],
i, len;
for( i = 0, len =versions.length; I < len; i++ ){
try{
new ActiveXObject( versions[i] );
arguments.callee.activeXString = version[ I ];
}catch(ex){
}
}
}
return new ActiveXObject(arguments.callee.activeXString );
}else {
throw new Error( “No XHR object available.” );
}
}
//创建XHR对象
var xhr = createXHR ( );
//设置http响应状态函数
/*onraedy属性表示请求/响应 过程的当前活动阶段，onready属性的值从一个值变为另一个值都会触发一次readystatechange事件*/
xhr.onreadystatechange = function (){
if(xhr.readyState == 4){
if(( xhr.state >= 200 )|| (xhr.state <= 300 ) || (xhr.state  == 304) ){
alert( xhr.respondText)
}else{
alert( “Request was unsuccessful :” + xhr.status );
}
}
};
//创建http请求
xhr.open( “传输方式”, “URL地址”, Boolean值 )；
//发送请求
xhr.send( );