ajax异步获取数据

function createXHR(){
	if( typeof XMLHttpRequest != "undefined" ){
		return new XMLHttpRequest();
	} else if( typeof ActiveXObject != "undefined" ){
		var version = [
			"MSXML2.XMLHttp.6.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp"
		];
		for( var i = 0; i < version.length; i++ ){
			try{
				return new ActiveXObject( version[ i ] );
			}catch( e ){
				// 跳过
			}
		}
	}else{
		throw new Error( "您的浏览器不支持XHR对象！" );
	}
}



// 异步
 $(function(){
	$("body").click(function(){
		var xhr = createXHR();
		xhr.onreadystatechange = function(){
			if( xhr.readyState == 4 ){   // 判断是否已经接受到全部响应数据
				if( xhr.status == 200 ){   // 判断是否返回成功
					alert( xhr.responseText );
				}else{
					throw new Error( "数据返回失败！状态代码：" + xhr.status + ",状态信息是:" + xhr.statusText );
				}
			}
		}
		xhr.open( "get","demo.PHP?rand=" + Math.random(),true );
		xhr.send(null);
		// xhr.abort();   // 取消异步请求
	});
});