Ionic 4 network check

Install network information plugin by using command:-

cordova plugin add cordova-plugin-network-information

Then you can use following code after deviceready to execute some code when the device goes offline :-

document.addEventListener("offline", onOffline, false);

function onOffline() {
    // Handle the offline event
    // use code to redirect here
}

You can try the official Ionic Network plugin (doc here).

Usage example from doc :

import { Network } from '@ionic-native/network/ngx'; //ngx

constructor(private network: Network) { }

...

// watch network for a disconnect
let disconnectSubscription = this.network.onDisconnect().subscribe(() => {
  console.log('network was disconnected :-(');
});

// stop disconnect watch
disconnectSubscription.unsubscribe();


// watch network for a connection
let connectSubscription = this.network.onConnect().subscribe(() => {
  console.log('network connected!');
  // We just got a connection but we need to wait briefly
   // before we determine the connection type. Might need to wait.
  // prior to doing any api requests as well.
  setTimeout(() => {
    if (this.network.type === 'wifi') {
      console.log('we got a wifi connection, woohoo!');
    }
  }, 3000);
});

// stop connect watch
connectSubscription.unsubscribe();

if (this.network.type === 'none') {
        this.presentAlert('network was disconnected :-(');
        setTimeout(() => {
            navigator['app'].exitApp();
        }, 4000);
}