function ajax(Url,sccuessFn,failureFn) {

	//1.创建XMLHttpRequest对象

	var xhr = null;

	if(window.XMLHttpRequest) {

		xhr = new XMLHttpRequest();

	}else {

		xhr = new ActiveXObject('Microsoft.XMLHTTP');

	}

	//2.打开与服务器的链接

	xhr = open('get',Url,true);

	//3.发送给服务器

	xhr = send(null);

	//4.响应就绪

	xhr.onreadystatechange = function() {

		if(xhr.readyState == 4) {

			if(xhr.status == 200) {

				successFn(xhr.responseText);

			}else {

				if(failureFn) {

					failureFn();

				}else {

					alert(xhr.status);

				}

			}

		}

	}

}