使用 html2canvas 将页面中某一部分转为图片下载

<div class="tc" v-for="(item,index) in qrcodeList" :key="index">
          <div :id="item.refname" class="poster " :class="item.bgimg">
            <div class="poster-dir">
              <div class="poster-title fontSize-3">问卷标题</div>
              <img class="qrcode" :src="qrcodeimg" >
              <div class="poster-own">问卷工厂提供技术支持</div>
            </div>
          </div>
          <span @click="downLoadCode(item.refname,‘问卷海报‘)" class="konbtn mt10">下载</span>
        </div>

downloadFile(data, fileName) {
      if (!data) {
        return;
      }
      let url = window.URL.createObjectURL(data);
      let link = document.createElement("a");
      link.style.display = "none";
      link.href = url;
      link.setAttribute("download", fileName);
      document.body.appendChild(link);
      link.click();
    },
    downLoadCode(id,name){
      html2canvas(document.getElementById(id),{useCORS:true,logging:true}).then(canvas => {
          canvas.toBlob(blob => {
          this.downloadFile(blob,name);
        }, "image/png");
      });
    },