<!DOCTYPE html>
<html>
<body>
<h2>Navigator 对象</h2>
<p>如果浏览器在线，则 onLine 属性返回 true：</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML =
"navigator.onLine is " + navigator.onLine;
</script>
</body>
</html>