function ajax(){   var ajaxData = {     type:arguments[0].type || "GET",     url:arguments[0].url || "",     async:arguments[0].async || "true",     data:arguments[0].data || null,     dataType:arguments[0].dataType || "text",     contentType:arguments[0].contentType || "application/x-www-form-urlencoded",     beforeSend:arguments[0].beforeSend || function(){},     success:arguments[0].success || function(){},     error:arguments[0].error || function(){}   }   ajaxData.beforeSend()   var xhr = createxmlHttpRequest();    xhr.responseType=ajaxData.dataType;   xhr.open(ajaxData.type,ajaxData.url,ajaxData.async);    xhr.setRequestHeader("Content-Type",ajaxData.contentType);    xhr.send(convertData(ajaxData.data));    xhr.onreadystatechange = function() {      if (xhr.readyState == 4) {        if(xhr.status == 200){         ajaxData.success(xhr.response)       }else{         ajaxData.error()       }      }   }  }  function createxmlHttpRequest() {    if (window.ActiveXObject) {      return new ActiveXObject("Microsoft.XMLHTTP");    } else if (window.XMLHttpRequest) {      return new XMLHttpRequest();    }  }  function convertData(data){   if( typeof data === 'object' ){     var convertResult = "" ;      for(var c in data){        convertResult+= c + "=" + data[c] + "&";      }      convertResult=convertResult.substring(0,convertResult.length-1)     return convertResult;   }else{     return data;   } } 

ajax({   type:"POST",   url:"ajax.php",   dataType:"json",   data:{"val1":"abc","val2":123,"val3":"456"},   beforeSend:function(){     //some js code   },   success:function(msg){     console.log(msg)   },   error:function(){     console.log("error")   } })