es6-11study/17/ajax.js

const p = new Promise((resolve,reject)=>{
    const xhr = new XMLHttpRequest()
    xhr.open("GET","https://api.apiopen.top/getJoke")
    xhr.send()
    xhr.onreadystatechange = function(){
        if(xhr.readyState === 4){
            if(xhr.status >= 200 && xhr.status < 300){
                resolve(xhr.response)
            }else{
                reject(xhr.status)
            }
        }
    }
})