下載圖片（vue 下載圖片）

downloadImg(){
        const url = this.imgUrl
        // window.open(_this.detail.imgUrl)
        let xmlhttp=new XMLHttpRequest();
        xmlhttp.open("GET",url,true);
        xmlhttp.responseType = "blob";
        xmlhttp.onload = function(){
          if (this.status == 200) {
            const blob = this.response;
            const link = document.createElement('a');
            link.href = window.URL.createObjectURL(blob);
            link.download = url.substring(url.lastIndexOf("/")+1, url.length);

            //此寫法兼容可火狐瀏覽器
            document.body.appendChild(link);

            const evt = document.createEvent("MouseEvents");
            evt.initEvent("click", false, false);
            link.dispatchEvent(evt);
            window.URL.revokeObjectURL(link.href)
            document.body.removeChild(link);
          };
        }

        xmlhttp.send();
      },