title: How to add/append string to blob in Google Apps Script (Google Drive API)
body: <p>This code does work, except this part <code>Drive.Files.update(thefile, theFileID, updatedBlob);</code></p>
  
  <pre><code>var folder = DriveApp.getFolderById("0B0RcUNcUERU5MGpIaEXXXXXXXX");
  var file = DriveApp.getFileById("NcUERXXXXXXXXERU5UWQUTZKY2X2"); 
  var file2 = DriveApp.getFileById("NcUERXXXXXXXXERU5UWDDDDDDD2"); 
  
  var myString = "sometext";
  var updatedBlob = file.getBlob() + myString;
  
  var myFileName = "StringAddedFile.mp4";  
  var thefile = {
    title: myFileName,
    mimeType: 'video/mp4'
  };
  
  var allFilesByName = folder.getFilesByName(myFileName);
  while (allFilesByName.hasNext()) {
    var thisFile = allFilesByName.next();
    var theFileID = thisFile.getId();
    var myVar = Drive.Files.update(thefile, theFileID, updatedBlob);
  };
  </code></pre>
  
  <p>I have tried:</p>
  
  <pre><code>file.getBlob() + myString;
  file.getBlob().getDataAsString() + myString;
  file.getBlob().getDataAsString() + file2.getBlob().getDataAsString();
  file.getAs() + file2.getAs();
  file.getBlob() + file2.getBlob();
  </code></pre>
  
  <p>...</p>
  
  <p>Getting this error message: <code>"The mediaData parameter only supports Blob types for upload."</code></p>
  
  <p>How can I add/append <code>myString</code> to <code>file</code>?</p>