I2C error Is there a way to thow and catch this error?

If you do:

try {
  I2C3.readFrom(...);
} catch (e) {
  console.log("Oops");
}

then it should work? your inability to catch the error might be because your External_Clk function is itself called from a timeout?

Worst case you can use uncaughtException, but that's a bit of a hack :) http://www.espruino.com/Reference#l_process_uncaughtException