手写一个AJAX
let request = new XMLHttpRequest()
request.open('POST','/xxx')
request.send()
request.onstatechange = ()=>{
if(request.readyState === 4){
if(request.status >=200 && request.status <300){
console.log('说明请求成功')
let string = request.responseText
let object = request.JSON.parse(string)
}else if(request.status > 400){
console.log('说明请求失败')
}
}
}