var http_request=false;
var returnTxt='';
function ajax(url) {
	http_request=false;
	if (window.XMLHttpRequest) {
		http_request=new XMLHttpRequest();
		if (http_request.overrideMimeType) http_request.overrideMimeType("text/xml");
	} else if (window.ActiveXObject) {
		try {
			http_request=new ActiveXObject("Msxml2.XMLHTTP");
		} catch (e) {
			try {
				http_request=new ActiveXObject("Microsoft.XMLHTTP");
			} catch (e) {}
		}
	}
	if (!http_request) {
		window.alert('创建AJAX会话失败');
		return false;
	}
	http_request.onreadystatechange=ajaxpro;
	http_request.open("GET",url,true);
	http_request.send(null);
}
function ajaxpro() {
	if (http_request.readyState==4) {
		if (http_request.status==200) {
			alert(http_request.responseText);
		} else alert('有错误发生');
	}
}