how to check app running in foreground or background in ionic/cordova/phonegap

For Ionic 2 and Ionic 3 the solution is:

import { Platform } from 'ionic-angular';

@Component({
  template: `OK`
})

constructor(public platform: Platform) {

    platform.ready().then(() => {

      if (platform.is('cordova')){

        //Subscribe on pause i.e. background
        this.platform.pause.subscribe(() => {
          //Hello pause
        });

        //Subscribe on resume i.e. foreground 
        this.platform.resume.subscribe(() => {
          window['paused'] = 0;
        });
       }
    });
}

A small service for Ionic based on Sithys answer:

factory('BackgroundCheck', function($ionicPlatform){
    var service = {};
    var inBackground = false;

    $ionicPlatform.ready(function() {        
        document.addEventListener("resume", function(){inBackground = false;}, false);
        document.addEventListener("pause", function(){inBackground = true;}, false);
    });

    service.isActive = function(){
        return inBackground == false;
    }
    return service;    
})

Use the two Events "Pause" and "Resume". You will find all Events here in the Apache Cordova Events Documentation.

Event - Pause:

  • The pause event fires when the native platform puts the application into the background, typically when the user switches to a different application.

Event - Resume

  • The resume event fires when the native platform pulls the application out from the background.

You can add an Eventlistener for that into your code. For those two Events that would be:

Pause - Quick Example

document.addEventListener("pause", onPause, false);

function onPause() {
    // Handle the pause event
}

Or Full Example like this:

<!DOCTYPE html>
<html>
  <head>
    <title>Pause Example</title>

    <script type="text/javascript" charset="utf-8" src="cordova.js"></script>
    <script type="text/javascript" charset="utf-8">

    // Wait for device API libraries to load
    //
    function onLoad() {
        document.addEventListener("deviceready", onDeviceReady, false);
    }

    // device APIs are available
    //
    function onDeviceReady() {
        document.addEventListener("pause", onPause, false);
    }

    // Handle the pause event
    //
    function onPause() {
    }

    </script>
  </head>
  <body onload="onLoad()">
  </body>
</html>

Resume - Quick Example

document.addEventListener("resume", onResume, false);

function onResume() {
    // Handle the resume event
}

Or Full Example like this

<!DOCTYPE html>
<html>
  <head>
    <title>Resume Example</title>

    <script type="text/javascript" charset="utf-8" src="cordova.js"></script>
    <script type="text/javascript" charset="utf-8">

    // Wait for device API libraries to load
    //
    function onLoad() {
        document.addEventListener("deviceready", onDeviceReady, false);
    }

    // device APIs are available
    //
    function onDeviceReady() {
        document.addEventListener("resume", onResume, false);
    }

    // Handle the resume event
    //
    function onResume() {
    }

    </script>
  </head>
  <body onload="onLoad()">
  </body>
</html>

Try that out and let me know, if you need further help!