e.js

if (typeof unreg !== 'undefined') unreg();

function logOnline() {
console.log('ONLINE', new Date().toLocaleTimeString())
}
function logOffline() {
console.log('offline', new Date().toLocaleTimeString())
}
function reg() {
window.addEventListener('online', logOnline);
window.addEventListener('offline', logOffline);
}
function unreg() {
window.removeEventListener('online', logOnline);
window.removeEventListener('offline', logOffline);
}
reg();