function querystring(obj) {
   
    var str = "";
    for (var arr in obj) {
   
    	//对传递的参数进行字符串拼接
        str += (arr + "=" + obj[arr] + "&");
    }
    //最后一位不取
    return str.substring(0, str.length - 1);
}


function $ajax({
   
    method = "get",
    url,
    data,
    success,
    error,
}) {
   
    var xhr = null;
    try {
   
        xhr = new XMLHttpRequest();
    } catch (error) {
   
        xhr = new ActiveXObject('Microsoft.XMLHTTP');
    }

    if (method == "get" && data != null) {
   
        url += "?" + querystring(data);
    }
    xhr.open(method, url, true);

    if (method == "get") {
   
        xhr.send();
    } else {
   
        xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded;charset=utf-8");
        xhr.send(querystring(data));
    }

    xhr.onreadystatechange = function () {
   
        if (xhr.readyState == 4) {
   
            if (xhr.status == 200) {
   
                if (success) {
   
                    success(xhr.responseText);
                }
            } else {
   
                if (error) {
   
                    error("error" + xhr.status);
                }
            }
        }
    }
}

使用

$ajax({
   
	url: "get.php",
	data: {
   
		uname: "taoyuhan",
		upwd: 123
	},
	success: function(res) {
   
		alert(res);
	},
	error: function(mes) {
   
		alert(mes);
	}
})