if you do something like:

  wait for data from fs.readfile 'test.txt'
  print data.toString

and readFile calls back with an error (the first argument is non-null), the error will be thrown just before the print statement. So print will not execute and you'll get a stack trace. The cool thing is that you can do these async calls within try blocks:

  try
    wait for data from fs.readfile 'test.txt'
    print data.toString()
    if data.length > 0
      wait for data2 from fs.readfile 'test2.txt'
      print data2.toString()
    else
      print 'too short'
  catch e
    print 'there was an error'
  wait for resp from db.save()

Will do what you expect - abort after either wait for if it fails and run the catch clause. Think about how you'd do that in JS:

  var error = null;
  var data, data2, resp;
  fs.readFile('test.txt', function (err, data) {
    if (err) return handleErr(err);
    console.log(data.toString())
    if (data.length > 0) {
      return fs.readFile('test2.txt', function (err, data2) {
        if (err) return handleErr(err);
        console.log(data2.toString());
        return closeout();
      });
    } else {
      console.log('too short');
      return closeout();
    }
  });
  function handleErr(err) {
    console.log('there was an error');
    return closeout();
  }
  function closeout() {
    return db.save(function (err, r) {
      if (err) throw err;
      resp = r;
    });
  }