問題描述:想通過 promise 對象來實現 ajax數據請求//getDate.json{"name":"zzz","age":22,"say":"hello zzz"}    //demo.js    let getJson = url =>{    let promise = new Promise((resolve,reject) =>{    let xhr = new XMLHttpRequest();        xhr.open("GET",url,true);        xhr.onreadystatechange = () =>{        if(this.readyState !== 4){            return;        }        if(this.status == 200){            resolve(this.response);        }else{            reject(new Error(this.statusText))        }    }    xhr.responseType = 'json';    xhr.setRequestHeader('Accept','application/json');    xhr.send(null);});    return promise;};getJson("getDate.json").then((json) =>{console.log(json);},(err)=>{console.log(err)});拋出錯誤:(intermediate value) is not a constructor