使用Promise封装ajax
const promiseAjax = (url,data)=>{
return new Promise((resolve,reject)=>{
const xhr = new XMLHttpRequest();
xhr.open(POST,url);
xhr.setRequestHeader('ContentType','application/json')
xhr.send(data)
xhr.onreadystatechange = function(){
if(xhr.readyState==4){
if(xhr.status>=200&&xhr.status<400){
resolve(xhr.response)
}else{
reject(xhr.status)
}
}
}
})
}