到目前为止，我们使用的所有示例都依赖于该getCurrentPosition()方法。但是，地理位置对象具有另一种方法watchPosition()，该方法允许您通过在位置更改时返回更新的位置来跟踪访客的运动。
的watchPosition()输入参数与相同getCurrentPosition()。但是，watchPosition()可能会多次触发成功函数-首次获取位置时，并且每次检测到新位置时都会触发一次。让我们看看它是如何工作的：
例试试这个代码»
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Watching Position</title>
<script>
// Set global variable
var watchID;
function showPosition() {
if(navigator.geolocation) {
watchID = navigator.geolocation.watchPosition(successCallback);
} else {
alert("Sorry, your browser does not support HTML5 geolocation.");
}
}
function successCallback(position) {
toggleWatchBtn.innerHTML = "Stop Watching";
// Check position has been changed or not before doing anything
if(prevLat != position.coords.latitude || prevLong != position.coords.longitude){
// Set previous location
var prevLat = position.coords.latitude;
var prevLong = position.coords.longitude;
// Get current position
var positionInfo = "Your current position is (" + "Latitude: " + position.coords.latitude + ", " + "Longitude: " + position.coords.longitude + ")";
document.getElementById("result").innerHTML = positionInfo;
}
}
function startWatch() {
var result = document.getElementById("result");
var toggleWatchBtn = document.getElementById("toggleWatchBtn");
toggleWatchBtn.onclick = function() {
if(watchID) {
toggleWatchBtn.innerHTML = "Start Watching";
navigator.geolocation.clearWatch(watchID);
watchID = false;
} else {
toggleWatchBtn.innerHTML = "Aquiring Geo Location...";
showPosition();
}
}
}
// Initialise the whole system (above)
window.onload = startWatch;
</script>
</head>
<body>
<button type="button" id="toggleWatchBtn">Start Watching</button>
<div id="result">
<!--Position information will be inserted here-->
</div>
</body>
</html>
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