NodeJS v8 "err": {"message": "fsReadFileAsync(...).then(...).then(...).catch(...).done is not a function",

After upgrading code and libraries, you might run into

"err":{"message":"fsReadFileAsync(...).then(...).then(...).catch(...).done is not a function",

An example erroneous code

 const fsReadFileAsync = util.promisify(fs.readFile.bind(fs));
 const fsWriteFileAsync = util.promisify(fs.writeFile.bind(fs));

 // First apply changes to fstab
 fsReadFileAsync(this._fstabFilename, "utf8")
 .then(function (contents) {
  var modifiedContents =
  self._alterFstab(
  contents,
  networkStorage.active,
  networkStorage.host,
  networkStorage.remotePath);
  return fsWriteFileAsync(self._fstabFilename, modifiedContents);
 })

 // Save our settings unless there was an error applying fstab changes
 .then(function () {
  self._saveSettings(networkStorage, callback);
 })

 .catch(function (error) {
  Helpers.Log.Error({
   fstabPath: self._fstabFilename,
   settings: networkStorage,
   error: error.stack
  }, "Error applying changes to fstab");
  callback(Errors.InternalServer());
 }).done();

Solution

Remove .done()

This happens when upgrading from var QFS = require("q-io/fs"); to native util.promisify()