accelerometer.watchAcceleration

At a regular interval, get the acceleration along the x, y, and z axis.

var watchID = navigator.accelerometer.watchAcceleration(accelerometerSuccess,
                                                       accelerometerError,
                                                       [accelerometerOptions]);

Description

The accelerometer is a motion sensor that detects the change (delta) in movement relative to the current position. The accelerometer can detect 3D movement along the x, y, and z axis.

The accelerometer.watchAcceleration gets the device's current acceleration at a regular interval. Each time the [Acceleration](acceleration/acceleration.html) is retrieved, the [accelerometerSuccess](parameters/accelerometerSuccess.html) callback function is executed. Specify the interval in milliseconds via the frequency parameter in the acceleratorOptions object.

The returned watch ID references references the accelerometer watch interval. The watch ID can be used with [accelerometer.clearWatch](accelerometer.clearWatch.html) to stop watching the accelerometer.

Supported Platforms

  • Android
  • BlackBerry WebWorks (OS 5.0 and higher)
  • iPhone
  • Windows Phone 7 (Mango)
  • Bada 1.2 & 2.x

Quick Example

function onSuccess(acceleration) {
    alert('Acceleration X: ' + acceleration.x + '\n' +
          'Acceleration Y: ' + acceleration.y + '\n' +
          'Acceleration Z: ' + acceleration.z + '\n' +
          'Timestamp: '      + acceleration.timestamp + '\n');
};

function onError() {
    alert('onError!');
};

var options = { frequency: 3000 };  // Update every 3 seconds

var watchID = navigator.accelerometer.watchAcceleration(onSuccess, onError, options);

Full Example

<!DOCTYPE html>
<html>
  <head>
    <title>Acceleration Example</title>

    <script type="text/javascript" charset="utf-8" src="cordova-1.8.1.js"></script>
    <script type="text/javascript" charset="utf-8">

    // The watch id references the current `watchAcceleration`
    var watchID = null;

    // Wait for Cordova to load
    //
    document.addEventListener("deviceready", onDeviceReady, false);

    // Cordova is ready
    //
    function onDeviceReady() {
        startWatch();
    }

    // Start watching the acceleration
    //
    function startWatch() {

        // Update acceleration every 3 seconds
        var options = { frequency: 3000 };

        watchID = navigator.accelerometer.watchAcceleration(onSuccess, onError, options);
    }

    // Stop watching the acceleration
    //
    function stopWatch() {
        if (watchID) {
            navigator.accelerometer.clearWatch(watchID);
            watchID = null;
        }
    }

    // onSuccess: Get a snapshot of the current acceleration
    //
    function onSuccess(acceleration) {
        var element = document.getElementById('accelerometer');
        element.innerHTML = 'Acceleration X: ' + acceleration.x + '<br />' +
                            'Acceleration Y: ' + acceleration.y + '<br />' +
                            'Acceleration Z: ' + acceleration.z + '<br />' +
                            'Timestamp: '      + acceleration.timestamp + '<br />';
    }

    // onError: Failed to get the acceleration
    //
    function onError() {
        alert('onError!');
    }

    </script>
  </head>
  <body>
    <div id="accelerometer">Waiting for accelerometer...</div>
  </body>
</html>

iPhone Quirks

  • At the interval requested, Cordova will call the success callback function and pass the accelerometer results.
  • However, in requests to the device Cordova restricts the interval to minimum of every 40ms and a maximum of every 1000ms.
    • For example, if you request an interval of 3 seconds (3000ms), Cordova will request an interval of 1 second from the device but invoke the success callback at the requested interval of 3 seconds.