trim last character from string?

If the value is actually a floating point number, but you're receiving a string, then you should be able to simply coerce the value to a number and the non-numeric characters will be discarded:

var ph = "8.55\r\n";

+ph === 8.55; // true

Unfortunately, that doesn't seem to work correctly in Espruino. I've filed a bug: https://github.com/espruino/Espruino/issues/268