function ajax(obj){
    if(typeof obj!="object"){
        console.error("参数类型错误");
        return;
    }
    var url=obj.url;
    if(obj.url==undefined){
        console.error("地址必须指定");
        return;
    }
    var type=obj.type||"get";
    var asynch=obj.asynch===undefined?true:obj.asynch;   //判断是否为异步连接
    var dataType=obj.dataType||"text";

//判断传入的数据类型
    var data=obj.data;
    if(typeof data=="object"){
        var temp="";
        for(var i in data){
            temp+=i+"="+data[i]+"&";
        }
        data=temp.slice(0,-1);
    }
//监听函数
    var xmlObj=window.XMLHttpRequest?new XMLHttpRequest():new ActiveXObject("Microsoft.XMLHTTP");
    xmlObj.onreadystatechange=function(){
        if(xmlObj.readyState==4){
            if(xmlObj.status==200){
                var result;
                if(dataType=="XML"){
                    result=xmlObj.responseXML;
                }else if(dataType=="json"){
                    result=eval("("+xmlObj.responseText+")");
                }else if(dataType=="text"){
                    result=xmlObj.responseText;
                }
                obj.success(result);
            }
        }
    }
//判断获取方式
    if(type=="get"){
        xmlObj.open("get",url+"?"+data,asynch);
        xmlObj.send()
    }else if(type=="post"){
        xmlObj.open("post",url,asynch);
        xmlObj.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
        xmlObj.send(data);
    }
}

基于promise的ajax

function ajax({ url = '', type = 'get', dataType = 'json', asynch = 'true' }) {
  return new Promise((resolve, reject) => {
    let xhr = new XMLHttpRequest();
    xhr.open(type, url, asynch);
    xhr.responseType = dataType;
    xhr.onload = function () { //xhr.readState=4 xhr.sratus=200
      if (xhr.status === 200) {
        resolve(xhr.response);
      } else {
        reject('error');
      }
    }
    xhr.onerror = function (err) {
      reject(err);
    }
    xhr.send();
  })
}