navigator.onLine still true when turning off WiFi, false when set "work offline" in browser

Question

navigator.onLine is still returning true when I turn off Wi-Fi (Airport on my notebook in OS X). This is counterintuitive behavior. But when I set "work offline" in a browser like Firefox, it correctly returns false. Is this expected?

alert(navigator.onLine ? "online" : "offline");

Answer 1

Yes. The browser doesn't provide network connectivity information to the page, but rather uses Work Offline's status as the value.

Answer 2

Use the window.addEventListener to detect network updates:

window.addEventListener('online',  amIOnline);
window.addEventListener('offline', amIOffline);

function amIOnline(){
    console.log('online');
}

function amIOffline(){
    console.log('offline');
}