function handleData(event) {
var buf = event.target.value.buffer;
if (buf.byteLength >= 20 ) {
// reading characteristic FFB1:
var str = String.fromCharCode.apply(null, new Uint8Array(buf));
console.log('I got ' + str);
} else {
// reading characteristic FFB2:
console.log(new Uint8Array(buf));
}
}