Detecting the current state of the network connection and responding to any changes that might occur, can be done by using one of several plugins. This example is about the cordova-plugin-network-information plugin.

Add the plugin to the project:

cordova plugin add cordova-plugin-network-information

After the Cordova deviceready event a connection object is available through navigator.connection. The type property contains the current network state:

document.addEventListener("deviceready", function() {
    var networkState = navigator.connection.type;
}, false);

networkState now contains one of the following constants:

Connection.UNKNOWN  //  Unknown connection
Connection.ETHERNET //  Ethernet connection
Connection.WIFI     //  WiFi connection
Connection.CELL_2G  //  Cell 2G connection
Connection.CELL_3G  //  Cell 3G connection
Connection.CELL_4G  //  Cell 4G connection
Connection.CELL     //  Cell generic connection
Connection.NONE     //  No network connection

Detecting a change in network connection can be done by hooking a function to either the online or the offline event:

document.addEventListener("online", function() {
    // device went online
    var networkState = navigator.connection.type; // Get new network state
    ...
}, false);

document.addEventListener("offline", function() {
    // device went offline
    var networkState = navigator.connection.type; // Get new network state
    ...
}, false);