// javascript document//表示 ajax 调用方式
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; version.length; i ++) {
			try {
				return new activexobject(version[i]);
			} catch (e) {
				//跳过
			}	
		}
	} else {
		throw new error('您的系统或浏览器不支持xhr对象！');
	}
}

//名值对转换为字符串
function paramsjoin(data) {
	var arr = [];
	for (var i in data) {
		arr.push(encodeuricomponent(i) + '=' + encodeuricomponent(data[i]));
	}
	return arr.join('&');
}


//封装ajax
function ajax(obj) {
	var xhr = createxhr();
	obj.url = obj.url + '?rand=' + math.random();
	obj.data = paramsjoin(obj.data);
	if (obj.method === 'get') obj.url += obj.url.indexof('?') == -1 ? '?' + obj.data : '&' + obj.data;
	if (obj.async === true) {
		xhr.onreadystatechange = function () {
			if (xhr.readystate == 4) {
				callback();
			}
		};
	}
	xhr.open(obj.method, obj.url, obj.async);
	if (obj.method === 'post') {
		xhr.setrequestheader('content-type', 'application/x-www-form-urlencoded');
		xhr.send(obj.data);	
	} else {
		xhr.send(null);
	}
	if (obj.async === false) {
		callback();
	}
	function callback() {
		if (xhr.status == 200) {
			obj.success(xhr.responsetext);			//回调传递参数
		} else {
			alert('获取数据错误！错误代号：' + xhr.status + '，错误信息：' + xhr.statustext);
		}	
	}
}