ajax获取XMLHttpRequest对象的通用方法

var http_request = false;

function createXmlHttpRequest(){
http_request = false;
if(window.XMLHttpRequest) { //Mozilla 浏览器
http_request = new XMLHttpRequest();
if (http_request.overrideMimeType) {//设置MiME类别
http_request.overrideMimeType("text/xml");
}
}else if (window.ActiveXObject) { // IE浏览器
try {
http_request = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
http_request = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e) {}
}
}
}

function XXXXX(){
createXmlHttpRequest();
if(!http_request){
window.alert("不能创建XMLHttpRequest对象实例.");
}else{
window.alert("创建XMLHttpRequest对象实例成功.");
}
}