ajax请求封装

function ajax(method,url,data="",dataType="json"){return new Promise((resolve,reject)=>{//1 获取xhrvar xhr= new XMLHttpRequest;//2 创建请求xhr.open(method,url,true);//3 设置请求头if(method=="post"){xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded";)}//4 设置回调xhr.onreadystatechange=function(){if(xhr.readyState==4)if(xhr.status==200){if(dataType=="json")resolve(JSON.parse(xhr.responseText));elseresolve(xhr.responseText);elsereject("请求出错:"+xhr.status);}}//5 发送xhr.send(data);})}