js ajax请求

/* 创建 XMLHttpRequest 对象 */
        var xmlHttp;
        function GetXmlHttpObject() {
            if (window.XMLHttpRequest) {
                // code for IE7+, Firefox, Chrome, Opera, Safari 
                xmlhttp = new XMLHttpRequest();
            } else {// code for IE6, IE5 
                xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
            }
            return xmlhttp;
        }
        // -----------ajax方法-----------// 
        function checkValidCode() {
            xmlHttp = GetXmlHttpObject();
            if (xmlHttp == null) {
                alert('您的浏览器不支持AJAX！');
                return;
            }
            var errorInfo = document.getElementById("errorShow");
            //当用户输入新的验证码内容时影藏用户名错误的提示
            errorInfo.hidden = true;
            var id = document.getElementById('checkCode').value;
            var url = "/checkValidCode/Index?id=" + id + "&t/" + Math.random();
            alert(id);
            xmlHttp.open("POST", url, true);
            xmlHttp.onreadystatechange = getOkGet;//发送事件后，收到信息了调用函数 
            xmlHttp.send();
        }
        function getOkGet() {
            if (xmlHttp.readyState == 1 || xmlHttp.readyState == 2 || xmlHttp.readyState == 3) {
                // 本地提示：加载中 
            }
            if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
                var d = xmlHttp.responseText;
                if(d!="true")
                {
                    var errorInfo = document.getElementById("errorShow");
                    var validError = document.getElementById("validCodeError");
                    var loginBtn = document.getElementById("loginBtn");
                    var pwdError = document.getElementById("error");
                    validError.hidden = false;
                    errorInfo.hidden = false;
                    pwdError.hidden = true;
                    loginBtn.disabled = false;
                }
            }
        }