Web Bluetooth / Automatic Reconnect (Async Await) Sample

Available in Chrome 55+ | 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 (Promises) sample.

Live Output


JavaScript Snippet

var bluetoothDevice;

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

async function connect() {
  exponentialBackoff(3 /* max retries */, 2 /* seconds delay */,
    async function toTry() {
      time('Connecting to Bluetooth Device... ');
      await 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.
async function exponentialBackoff(max, delay, toTry, success, fail) {
  try {
    const result = await toTry();
    success(result);
  } catch(error) {
    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);
}