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Navigator: onLine property

Returns the online status of the browser. The property returns a boolean value, with true meaning online and false meaning offline. The property sends updates whenever the browser's ability to connect to the network changes. The update occurs when the user follows links or when a script requests a remote page. For example, the property should return false when users click links soon after they lose internet connection.

Browsers implement this property differently.

In Chrome and Safari, if the browser is not able to connect to a local area network (LAN) or a router, it is offline; all other conditions return true. So while you can assume that the browser is offline when it returns a false value, you cannot assume that a true value necessarily means that the browser can access the internet. You could be getting false positives, such as in cases where the computer is running a virtualization software that has virtual ethernet adapters that are always "connected." Therefore, if you really want to determine the online status of the browser, you should develop additional means for checking.

In Firefox, switching the browser to offline mode sends a false value. Until Firefox 41, all other conditions returned a true value; testing actual behavior on Nightly 68 on Windows shows that it only looks for LAN connection like Chrome and Safari giving false positives.

You can see changes in the network state by listening to the online and offline events.

Value

A boolean.

Examples

Basic usage

To check if you are online, query window.navigator.onLine, as in the following example:

js

if (navigator.onLine) {
  console.log("online");
} else {
  console.log("offline");
}

If the browser doesn't support navigator.onLine the above example will always come out as false/undefined.

Listening for changes in network status

To see changes in the network state, use addEventListener to listen for the events on window.online and window.offline, as in the following example:

js

window.addEventListener("offline", (e) => {
  console.log("offline");
});

window.addEventListener("online", (e) => {
  console.log("online");
});

Specifications

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
onLine
2Earlier versions of Chrome incorrectly return true when a tab is first opened, but it starts reporting the correct connectivity status after the first network event. Windows: 11, macOS: 14, Chrome OS: 13, Linux: Always returns true. For history, see crbug.com/7469.
12
1.5Since Firefox 4 the browser returns true when 'Work Offline' mode is disabled and false when it is enabled, regardless of actual connectivity. Since Firefox 41, on OS X and Windows, the returned values follow the actual network connectivity, unless 'Work offline' mode is selected (where it will always return false).
4in Internet Explorer 8 'online' and 'offline' events are raised on the document.body; under IE 9 they are raised on both document.body and window.
3From Opera 11.1 until Opera 12.1, the browser returns true when 'Work Offline' mode is disabled and false when it is enabled, regardless of actual connectivity.
4
≤37Can incorrectly return true, see bug 811122.
18 4
10.1From Opera 11.1 until Opera 12.1, the browser returns true when 'Work Offline' mode is disabled and false when it is enabled, regardless of actual connectivity.
3.2 1.0

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https://developer.mozilla.org/en-US/docs/Web/API/Navigator/onLine