Creating the file based on the base64

fileHelpers.ts

function base64ToArrayBuffer(base64Str: string) {
  const byteCharacters = window.atob(base64Str);
  const byteNumbers = new Array(byteCharacters.length);
  for (let i = 0; i < byteCharacters.length; i++) {
    byteNumbers[i] = byteCharacters.charCodeAt(i);
  }
  const byteArray = new Uint8Array(byteNumbers);

  return byteArray;
}

function showDocument(base64Str: string, mimeType: string) {
  const byteArray = base64ToArrayBuffer(base64Str);
  const file = new Blob([byteArray], { type: mimeType + ';base64' });
  const fileURL = URL.createObjectURL(file);
  window.open(fileURL);
}