当网络浏览器开始离线工作时，onoffline 属性就会触发。您可以尝试运行以下代码来实现onoffline 属性 -
<!DOCTYPE html>
<html>
<body ononline = "onlineFunc()" onoffline = "offlineFunc()">
<script>
function onlineFunc() {
alert ("Working online!");
}
function offlineFunc() {
alert ("Workinf offline!");
}
</script>
<p>Got o the web browser menu bar and click the File menu. Select "Work Offline" and toggle between online and offline.</p>
</body>
</html>
