Web Bluetooth / Automatic Reconnect Sample

Available in Chrome 52+ | View on GitHub | Browse Samples

The Web Bluetooth API lets websites discover and communicate with devices over the Bluetooth 4 wireless standard using the Generic Attribute Profile (GATT). It is currently partially implemented in Android M, Chrome OS, Linux, and Mac.

This sample illustrates the use of the Web Bluetooth API to reconnect to a disconnected Bluetooth device using a simple exponential backoff algorithm. You may want to check out the Automatic Reconnect (Async Await) sample.

Live Output


JavaScript Snippet

var bluetoothDevice;

function onButtonClick() {
  bluetoothDevice = null;
  log('Requesting any Bluetooth Device...');
  navigator.bluetooth.requestDevice({
     // filters: [...] <- Prefer filters to save energy & show relevant devices.
     acceptAllDevices: true})
  .then(device => {
    bluetoothDevice = device;
    bluetoothDevice.addEventListener('gattserverdisconnected', onDisconnected);
    connect();
  })
  .catch(error => {
    log('Argh! ' + error);
  });
}

function connect() {
  exponentialBackoff(3 /* max retries */, 2 /* seconds delay */,
    function toTry() {
      time('Connecting to Bluetooth Device... ');
      return bluetoothDevice.gatt.connect();
    },
    function success() {
      log('> Bluetooth Device connected. Try disconnect it now.');
    },
    function fail() {
      time('Failed to reconnect.');
    });
}

function onDisconnected() {
  log('> Bluetooth Device disconnected');
  connect();
}

/* Utils */

// This function keeps calling "toTry" until promise resolves or has
// retried "max" number of times. First retry has a delay of "delay" seconds.
// "success" is called upon success.
function exponentialBackoff(max, delay, toTry, success, fail) {
  toTry().then(result => success(result))
  .catch(_ => {
    if (max === 0) {
      return fail();
    }
    time('Retrying in ' + delay + 's... (' + max + ' tries left)');
    setTimeout(function() {
      exponentialBackoff(--max, delay * 2, toTry, success, fail);
    }, delay * 1000);
  });
}

function time(text) {
  log('[' + new Date().toJSON().substr(11, 8) + '] ' + text);
}