qz_hid_scale.html

<script src="https://unpkg.com/qz-tray"></script>
<script src="https://unpkg.com/qz-sift"></script>

<label for="lb">lb: </label><input id="lb" type="text" readonly/>
<label for="oz">oz: </label><input id="oz" type="text" readonly/>

<script>
// The callback code when a response is received
qz.hid.setHidCallbacks(function (event) {
   if(event.type === 'RECEIVE') {
	 var parsed = sift.parse.scale(event.output);
     if(parsed.valid) {
        if(parsed.units.value == 'lb') {
            document.getElementById('lb').value = parsed.weight.value;
            document.getElementById('oz').value = parsed.weight.value * 16;
        } else {
            document.getElementById('lb').value = "Wrong units!";
            console.warn("Value:", parsed);
        }
     }
   } else {
      document.getElementById('lb').value = 'ERROR';
      document.getElementById('oz').value = 'ERROR';
   }
});

// Scale manufacturer.  0x0eb8|0xf000 = Mettler Toledo
var device = { vendorId: '0x0eb8', productId: '0xf000' };
device.interval = 25; // interval between reads, in milliseconds
device.responseSize = 8; // response size, in bytes

qz.websocket.connect().then(() => {
	return qz.hid.claimDevice(device);
}).then(() => {
	return qz.hid.openStream(device);
}).catch(err => alert(err));

</script>