AJAX之验证某个表单项在数据库中唯一

在使用AJAX的时候不免要验证用户提交的数据在数据库中是否唯一（比如：用户名，电子邮件等），请看一个简单的实现：

/*
 *  awx
 *
 *
 *
/*--------------------------------------------------------------------------*/
    /**
     *how to define obj
     *obj = {name:"the param's name, id as default",
     *       value:"the param's value,",
     *       feedback:"the data area id to show the check result"
     *      }
     *
     *how to use it
     *    checkMethod('url',obj)
     *
     *    for this ,we can use it in jsp/html.. like this:
     *    checkMethod("/check.do",{name:'id',value:'id_value',feedback:'feedback'});
     */

    function checkMethod(url,obj/*The request parameter object has name and value fields*/){
      obj = checkPairObject(obj);
      if(obj.value !=""){
         document.getElementById(obj.feedback).innerHTML = "请稍候…………";
         send_request(url,obj);
      } else {
         alert("输入信息不能为空!");
      }
    }

    function checkPairObject(obj){
      if(obj==null)obj = {};
      var name = obj.name;
      var value = obj.value;
      var feedback = obj.feedback;
      if(obj.name == null){
        obj.name = "id";
      }
      if(obj.value== null){
        obj.value="";
      }
      if(obj.feedback==null){
        obj.feedback="feedback";
      }
      return obj;
    }

    var http_request = false;

    function createPostParam(obj/*object to generate name and value and returned text area id */){
      obj = checkPairObject(obj);
      var pair_param = obj.name+"="+obj.value;
      return pair_param;
    }

    function send_request(url,obj) {
        var queryString = createPostParam(obj);
        http_request = false;
        if(window.XMLHttpRequest) { //Mozilla
            http_request = new XMLHttpRequest();
            if (http_request.overrideMimeType) {//MiME
                http_request.overrideMimeType('text/xml');
            }
        }
        else if (window.ActiveXObject) { // IE
            try {
                http_request = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
                try {
                    http_request = new ActiveXObject("Microsoft.XMLHTTP");
                } catch (e) {}
            }
        }
        if (!http_request) { //
            return false;
        }
        http_request.open("POST", url, true);
        http_request.onreadystatechange = function(){processRequest(obj.feedback);}
        http_request.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
        http_request.send(queryString);
    }

    function processRequest(show_return_area_id) {
        var f = document.form1;
        if (http_request.readyState == 4) {
            if (http_request.status == 200) {
                var returnStr = http_request.responseText;
                if(returnStr.indexOf("Error")==-1) {
                    document.getElementById(show_return_area_id).innerHTML ="";
                    alert(returnStr);
                }
                else {
                    document.getElementById(show_return_area_id).innerHTML ="";
                    alert(returnStr);
                }
            } else {
                   document.getElementById(show_return_area_id).innerHTML = "";
                   alert("数据传输错误，稍后请重试!");
            }
        }
    }