trim last character from string?

I think your issue was e.data != "\r" || e.data != "\n" because it'll always be true - it should be e.data != "\r" && e.data != "\n"

I guess the thing to do is to use the \r as a signal that the data has ended:

if (e.data == "\r" || e.data == "\n") {
  print(myValue);
  myValue="";
} else {
  myValue+=e.data;
}