js base64轉下載文件

// base64轉Blob
var dataURLtoBlob = function(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 });
}
// base64轉downloadfile
var dataURLtoDownload = function(dataurl, name) {
  let blob = dataURLtoBlob(dataurl)
  let url = URL.createObjectURL(blob)
  let save_link = document.createElementNS("http://www.w3.org/1999/xhtml", "a")
  save_link.href = url
  save_link.download = name;
  save_link.click()
}

// 使用
// 下載文件
dataURLtoDownload('base64數據','文件名.txt')