[js] 写个方法将base64的数据流装换为二进制流

/**

• Base64字符串转二进制流
• @param {String} dataurl Base64字符串(字符串包含Data URI scheme，例如：data:image/png;base64, )
  /
  function dataURLtoBlob(dataurl) {
  var arr = dataurl.split(","),
  mime = arr[0].match(/:(.?);/)[1],
  bstr = atob(arr[1]),
  n = bstr.length,
  u8arr = new Uint8Array(n);
  while (n--) {
  u8arr[n] = bstr.charCodeAt(n);
  }
  return new Blob([u8arr], {
  type: mime,
  });
  }
  let dataurl = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAQAAAADCAIAAAA7ljmRAAAAGElEQVQIW2P4DwcMDAxAfBvMAhEQMYgcACEHG8ELxtbPAAAAAElFTkSuQmCC';
  let blob = dataURLtoBlob(dataurl);