使用原生JS写出一个AJAX请求

let request = new XMLHttpRequest()
    request.open('get','xxx')
    request.send()
    request.onreadystatechange = ()=>{
        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 = window.JSON.parse(string)
            }
        }else if(request.status >= 400){
            console.log('说明请求失败')
        }