Espruino original <> ESP32 serial communication

Yes, I'd always buffer it. I think it's pretty common practice to just use the newline character:

function handleLine(l) {...}
function setup() {
  Serial2.setup(115200);
  var line="";
  Serial2.on('data', function (str) {
    var l = (line+str).split("\n");
    line = l.pop();
    l.forEach(handleLine);
  });
};