手写AJAX

AJAX async JavaScript and XML(JSON) 一般工作中用封装好的函数发送请求，如： Axios jQuery VueResource window.fetch

但面试中需要会手写AJAX:

const request = new XMLHttpRequest()
request.open('GET','/xxx')
request.onreadystatechange=()=>{
    if(request.readyState ===4){
        if(request.status >=200 && request.status <300 || request.status ===304){
            success(request)
        }else{
            fail(request)
        }
    }
    
}
request.send('{"name":"jackson"}')

XMLHttpRequest.readyState developer.mozilla.org/zh-CN/docs/…