//data作为参数传入我们下面封装的函数
var data = {
       //数据
       user:"yonghu1",
       pass:'12345',
       age:18,
       //回调函数
       success:function (data){
        alert(data);
       }
      }

function toData(obj){
  if (obj == null){
    return obj;
  }
  var arr = [];
  for (var i in obj){
    var str = i+"="+obj[i];
    arr.push(str);
  }
  return arr.join("&");
}

function ajax(obj){
  //指定提交方式的默认值
  obj.type = obj.type || "get";
  //设置是否异步，默认为true(异步)
  obj.async = obj.async || true;
  //设置数据的默认值
  obj.data = obj.data || null;
  if (window.XMLHttpRequest){
    //非ie
    var ajax = new XMLHttpRequest();
  }else{
    //ie
    var ajax = new ActiveXObject("Microsoft.XMLHTTP");
  }
  //区分get和post
  if (obj.type == "post"){
    ajax.open(obj.type,obj.url,obj.async);
    ajax.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    var data = toData(obj.data);
    ajax.send(data);
  }else{
    //get test.php?xx=xx&aa=xx
    var url = obj.url+"?"+toData(obj.data);
    ajax.open(obj.type,url,obj.async);
    ajax.send();
  }

  ajax.onreadystatechange = function (){
    if (ajax.readyState == 4){
        if (ajax.status>=200&&ajax.status<300 || ajax.status==304){
          if (obj.success){
            obj.success(ajax.responseText);
          }
        }else{
          if (obj.error){
            obj.error(ajax.status);
          }
        }
      }
   }  
}