To check whether a user is online or offline in JavaScript, You have to listen for the events online and offline on the window in JavaScript.
Check if User is online
Add an online event listener to the window like this,
// to check if user is online
// add an online event listener
// to window
window.addEventListener("online", (event) => {
console.log("User is Online ✅");
});
Check if User is offline
Add an offline event listener to the window like this,
// to check if user is offline
// add an offline event listener
// to window
window.addEventListener("offline", (event) => {
console.log("User is Offline 🚫");
});