取消HTML5中正在进行的watchPosition调用
clearWatch方法取消正在进行的watchPosition调用。取消后，watchPosition调用将停止检索有关设备当前地理位置的更新。
<!DOCTYPE HTML>
<html>
<head>
<script>
var watchID;
var geoLoc;
function showLocation(position) {
var latitude = position.coords.latitude;
var longitude = position.coords.longitude;
alert("Latitude : " + latitude + " Longitude: " + longitude);
}
function errorHandler(err) {
if(err.code == 1) {
alert("Error: Access is denied!");
}
else if( err.code == 2) {
alert("Error: Position is unavailable!");
}
}
function getLocationUpdate(){
if(navigator.geolocation){
//超时为60000毫秒（60秒）
var options = {timeout:60000};
geoLoc = navigator.geolocation;
watchID = geoLoc.watchPosition(showLocation, errorHandler, options);
}
else{
alert("Sorry, browser does not support geolocation!");
}
}
function stopWatch(){
geoLoc.clearWatch(watchID);
}
</script>
</head>
<body>
<form>
<input type = "button" onclick = "getLocationUpdate();" value = "Watch Update"/>
<input type = "button" onclick = "stopWatch();" value = "Stop Watch"/>
</form>
</body>
</html>