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demo.js
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demo.js
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var myCharacteristic;
function onStartButtonClick() {
let serviceUuid = 'heart_rate'; // document.querySelector('#service').value;
if (serviceUuid.startsWith('0x')) {
serviceUuid = parseInt(serviceUuid);
}
let characteristicUuid = 'heart_rate_measurement'; // document.querySelector('#characteristic').value;
if (characteristicUuid.startsWith('0x')) {
characteristicUuid = parseInt(characteristicUuid);
}
console.log('Requesting Bluetooth Device...');
navigator.bluetooth.requestDevice({filters: [{services: [serviceUuid]}]})
.then(device => {
console.log('Connecting to GATT Server...');
return device.gatt.connect();
})
.then(server => {
console.log('Getting Service...');
return server.getPrimaryService(serviceUuid);
})
.then(service => {
console.log('Getting Characteristic...');
return service.getCharacteristic(characteristicUuid);
})
.then(characteristic => {
myCharacteristic = characteristic;
return myCharacteristic.startNotifications().then(_ => {
console.log('> Notifications started');
myCharacteristic.addEventListener('characteristicvaluechanged',
handleNotifications);
});
})
.catch(error => {
console.log('Argh! ' + error);
});
}
function onStopButtonClick() {
if (myCharacteristic) {
myCharacteristic.stopNotifications()
.then(_ => {
console.log('> Notifications stopped');
myCharacteristic.removeEventListener('characteristicvaluechanged',
handleNotifications);
})
.catch(error => {
console.log('Argh! ' + error);
});
}
}
function handleNotifications(event) {
let value = event.target.value;
const {heartRate, rrIntervals} = parseHeartRate(value);
console.log('> ' + JSON.stringify({
time: Date.now(),
heartRate,
rrIntervals,
}));
}
function isWebBluetoothEnabled() {
if (navigator.bluetooth) {
return true;
} else {
console.error('Web Bluetooth API is not available.\n' +
'Please make sure the Web Bluetooth flag is enabled.');
return false;
}
}
function parseHeartRate(data) {
let flags = data.getUint8(0);
let rate16Bits = flags & 0x1;
let result = {};
let index = 1;
if (rate16Bits) {
result.heartRate = data.getUint16(index, /*littleEndian=*/true);
index += 2;
} else {
result.heartRate = data.getUint8(index);
index += 1;
}
let contactDetected = flags & 0x2;
let contactSensorPresent = flags & 0x4;
if (contactSensorPresent) {
result.contactDetected = !!contactDetected;
}
let energyPresent = flags & 0x8;
if (energyPresent) {
result.energyExpended = data.getUint16(index, /*littleEndian=*/true);
index += 2;
}
let rrIntervalPresent = flags & 0x10;
if (rrIntervalPresent) {
let rrIntervals = [];
for (; index + 1 < data.byteLength; index += 2) {
rrIntervals.push(data.getUint16(index, /*littleEndian=*/true));
}
result.rrIntervals = rrIntervals;
}
return result;
}
document.querySelector('#startNotifications').addEventListener('click', event => {
event.stopPropagation();
event.preventDefault();
if (isWebBluetoothEnabled()) {
console.clear();
onStartButtonClick();
}
});