navigator.onLine is a read-only Navigator property that returns a Boolean: true when the browser thinks the device is online, false when offline (MDN). When the value changes, window fires online or offline.
Read the notes below before you rely on this property. Prefer feature detection when support is limited.
Use navigator.onLine. Start with this line.
navigator.onLine| Call | What it does |
|---|---|
navigator.onLine | Primary signature. |
Built into the browser. Read navigator.onLine on Navigator — no import required.
navigator.onLine| Parameter | Description |
|---|---|
| Request error handling | Required. Truth about reachability |
| Return Value | Description |
|---|---|
| * | The current value of navigator.onLine. |
onLinePrint the current Boolean status.
console.log(navigator.onLine);true means “thinks online.” Not proof of Internet.false means “thinks offline.” Still verify with real requests.if / else (MDN)Branch on the current status with MDN’s basic pattern.
if (navigator.onLine) {
console.log("online");
} else {
console.log("offline");
}true takes the online branch.online / offline EventsListen on window when the browser flips network status.
window.addEventListener("offline", () => {
console.log("offline");
});
window.addEventListener("online", () => {
console.log("online");
});
console.log("listeners ready; current: " + navigator.onLine);window. MDN listens for both event names.Show a message without hard-disabling the rest of the app.
function networkHint() {
if (navigator.onLine) {
return "Connected (hint) — still handle request errors";
}
return "You may be offline — changes can sync later";
}
console.log(networkHint());One small helper returns label + Boolean and wires listeners.
function watchNetwork(onChange) {
function report() {
const online = navigator.onLine;
onChange({
online: online,
label: online ? "online" : "offline"
});
}
window.addEventListener("online", report);
window.addEventListener("offline", report);
report();
return function stop() {
window.removeEventListener("online", report);
window.removeEventListener("offline", report);
};
}
watchNetwork((info) => {
console.log(JSON.stringify(info));
});report.stop. Remove listeners when the UI unmounts.navigator.onLine is Baseline Widely available (MDN, since about July 2015). The online / offline window events are widely supported too.
Supported across modern Chrome, Firefox, Safari, Edge, and Opera. Heuristics differ by OS — treat the Boolean as a hint.
Bottom line: Safe to read everywhere for UX hints. Pair with window events and real request error handling.
Learn how navigator.oscpu exposes a legacy OS/CPU string.
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