blob格式下载文件通用方法

      console.log("下载文件内容", this.content)
      const blob = new Blob([this.content], {type: 'text/plain;charset=utf-8'})

      let downloadElement = document.createElement('a');
      let href = window.URL.createObjectURL(blob);           //创建下载的链接
      downloadElement.href = href;
      let time = (new Date()).valueOf();
      downloadElement.download = '代码库' + time + '.java'; //下载后文件名
      document.body.appendChild(downloadElement);
      downloadElement.click();                               //点击下载
      document.body.removeChild(downloadElement);            //下载完成移除元素
      window.URL.revokeObjectURL(href);                      //释放掉blob对象