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snippets/use-navigator-on-line.md

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+---
+title: React useNavigatorOnLine hook
+tags: hooks,state,effect
+author: chalarangelo
+cover: digital-nomad-7
+firstSeen: 2019-09-11T09:17:26+03:00
+lastUpdated: 2020-11-16T14:17:53+02:00
+---
+
+Checks if the client is online or offline.
+
+- Create a function, `getOnLineStatus`, that uses the `Navigator.onLine` web API to get the online status of the client.
+- Use the `useState()` hook to create an appropriate state variable, `status`, and setter.
+- Use the `useEffect()` hook to add listeners for appropriate events, updating state, and cleanup those listeners when unmounting.
+- Finally return the `status` state variable.
+
+```jsx
+const getOnLineStatus = () =>
+  typeof navigator !== 'undefined' && typeof navigator.onLine === 'boolean'
+    ? navigator.onLine
+    : true;
+
+const useNavigatorOnLine = () => {
+  const [status, setStatus] = React.useState(getOnLineStatus());
+
+  const setOnline = () => setStatus(true);
+  const setOffline = () => setStatus(false);
+
+  React.useEffect(() => {
+    window.addEventListener('online', setOnline);
+    window.addEventListener('offline', setOffline);
+
+    return () => {
+      window.removeEventListener('online', setOnline);
+      window.removeEventListener('offline', setOffline);
+    };
+  }, []);
+
+  return status;
+};
+```
+
+```jsx
+const StatusIndicator = () => {
+  const isOnline = useNavigatorOnLine();
+
+  return <span>You are {isOnline ? 'online' : 'offline'}.</span>;
+};
+
+ReactDOM.createRoot(document.getElementById('root')).render(
+  <StatusIndicator />
+);
+```