DownloadFile(base64Stream, fileName) + IE Compatibility

/**
 * Download a file by creating a hidden hyperlink DOM element in the current page,
 * using file location as URL, and triggering a click on it.
 * Confirmation dialog box and actual download is then handled directly by the navigator.
 *
 * @param {String} base64Stream Radix-64 binary data represented as an ASCII string
 * @param {String} fileName     Desired output file name
 */
export function downloadFile(base64Stream, fileName) {
  saveByteArray([base64ToArrayBuffer(base64Stream)], fileName);
}

function base64ToArrayBuffer(base64) {
  const binaryString = window.atob(base64);
  const binaryLen    = binaryString.length;
  const bytes        = new Uint8Array(binaryLen);

  for (let i = 0; i < binaryLen; i++) {
    bytes[i] = binaryString.charCodeAt(i);
  }

  return bytes;
}

function saveByteArray(data, name) {
  const blob = new Blob(data, { type : 'octet/stream' });

  // Download for IE
  if (window.navigator && window.navigator.msSaveOrOpenBlob) {
    window.navigator.msSaveOrOpenBlob(blob, name);
    return;
  }

  // Download for other browsers
  const a = document.createElement('a');

  document.body.appendChild(a);
  a.style = 'display: none';

  const url = window.URL.createObjectURL(blob);

  a.href     = url;
  a.download = name;
  a.click();
  window.URL.revokeObjectURL(url);
}