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At a regular interval, get the compass heading in degrees.
var watchID = navigator.compass.watchHeading(compassSuccess, compassError, [compassOptions]);
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 the compass watch interval. The watch ID can be used with compass.clearWatch to stop watching the compass.
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);
<!DOCTYPE html>
<html>
<head>
<title>Compass Example</title>
<script type="text/javascript" charset="utf-8" src="cordova-x.x.x.js"></script>
<script type="text/javascript" charset="utf-8">
// The watch id references the current `watchHeading`
var watchID = null;
// Wait for device API libraries to load
//
document.addEventListener("deviceready", onDeviceReady, false);
// device APIs are available
//
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>
In iOS compass.watchHeading can also get the device's current heading when it changes by a specified number of degrees. Each time the heading changes by the specified number of degrees or more, the headingSuccess callback function executes. Specify the degrees of change via the filter parameter in the compassOptions object. Clear the watch as usual by passing the returned watch ID to compass.clearWatch. This functionality replaces the previously separate, iOS-only watchHeadingFilter and clearWatchFilter functions, which were removed in version 1.6.
Only one watchHeading can be in effect at one time in iOS. If a watchHeading uses a filter, calling getCurrentHeading or watchHeading uses the existing filter value to specify heading changes. Watching heading changes with a filter is more efficient than with time intervals.