Google apps script to turn a google doc from markdown code to formatted google doc

Code.gs

function convertFromMarkdown(file_idz) {
  // Ensure the Google Drive Advanced Service is enabled (Steps below)

  // Get the ID of the Google Doc to be updated
  var file_id = file_idz || "put_a_default_id_here_if_you_want";
  
  // Open the document to read its content
  const docFile = DocumentApp.openById(file_id);
  const markdownContent = docFile.getBody().getText();
  
  // Create a blob with the markdown content.
  // The MimeType 'text/markdown' is crucial for Drive to recognize it as markdown.
  const blob = Utilities.newBlob(markdownContent, 'text/markdown');
  
  // Update the existing Google Doc with the new content.
  // The 'convert: true' option tells Google Drive to convert the incoming blob
  // (which is markdown) into a Google Docs format.
  const updatedFile = Drive.Files.update(
    {}, // Resource body: We're not changing file metadata (like name or parent), just content.
    file_id, // The ID of the file to update
    blob, // The new content (markdown blob)
    {
      convert: true, // This is key: tells Drive to convert the markdown blob into Google Doc format
      supportsAllDrives: true // Required if your file might be on a Shared Drive
    }
  );

  // Return the ID of the updated file (which is the same as the original file_id)
  return updatedFile.id;
}