compass.watchHeading

At a regular interval, get the compass heading in degrees.

var watchID = navigator.compass.watchHeading(compassSuccess, compassError, [compassOptions]);

Description

The compass is a sensor that detects the direction or heading that the device is pointed. It measures the heading in degrees from 0 to 359.99.

The compass.watchHeading gets the device's current heading at a regular interval. Each time the heading is retrieved, the headingSuccess callback function is executed. Specify the interval in milliseconds via the frequency parameter in the compassOptions object.

The returned watch ID references references the compass watch interval. The watch ID can be used with compass.clearWatch to stop watching the compass.

Supported Platforms

Android
iPhone
Windows Phone 7 ( Mango ) if available in hardware

Quick Example

function onSuccess(heading) {
    var element = document.getElementById('heading');
    element.innerHTML = 'Heading: ' + heading.magneticHeading;
};

function onError(compassError) {
        alert('Compass error: ' + compassError.code);
};

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

var watchID = navigator.compass.watchHeading(onSuccess, onError, options);

Full Example

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

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

    // The watch id references the current `watchHeading`
    var watchID = null;
    
    // Wait for PhoneGap to load
    //
    document.addEventListener("deviceready", onDeviceReady, false);

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

    // Start watching the compass
    //
    function startWatch() {
        
        // Update compass every 3 seconds
        var options = { frequency: 3000 };
        
        watchID = navigator.compass.watchHeading(onSuccess, onError, options);
    }
    
    // Stop watching the compass
    //
    function stopWatch() {
        if (watchID) {
            navigator.compass.clearWatch(watchID);
            watchID = null;
        }
    }
    
    // onSuccess: Get the current heading
    //
    function onSuccess(heading) {
        var element = document.getElementById('heading');
        element.innerHTML = 'Heading: ' + heading.magneticHeading;
    }

    // onError: Failed to get the heading
    //
    function onError(compassError) {
        alert('Compass error: ' + compassError.code);
    }

    </script>
  </head>
  <body>
    <div id="heading">Waiting for heading...</div>
    <button onclick="startWatch();">Start Watching</button>
    <button onclick="stopWatch();">Stop Watching</button>
  </body>
</html>