Just enable the console logs in the emulator. Here my example:

> ionic emulate ios --livereload

  Setup Live Reload
  Running dev server: http://localhost:8100
  Adding in default Ionic hooks
  Running live reload server: http://localhost:35729
  Watching : [ 'www/**/*', '!www/lib/**/*' ]
  Ionic server commands, enter:
    restart or r to restart the client app from the root
    goto or g and a url to have the app navigate to the given url
    consolelogs or c to enable/disable console log output
    serverlogs or s to enable/disable server log output
    quit or q to shutdown the server and exit

Type consolelogs in the command line and hit enter.

  consolelogs

  Console log output: enabled
  Loading: /?restart=382451
  ionic $ 0     498458   log      Hi there! This is from console.log

run ionic emulate ios -l -c

This will open the emulator with livereload feature, and you'll see all the console logs in the terminal. To turn the console logs off (or on) just write consolelogs or just c in the terminal while the ionic server is running

Another very convenient way to debug your app when using iOS emulator/device is using the Safari developer tools

When the app runs - enter Safari and choose "Develop > iOS Simulator > your page"

If you work with a real device you'll see the device's name instead of "iOS Simulator"

If you don't see the "Develop" menu in safari - enter Safari's preferences and enable it from the "advanced" tab

1. If you wan't to watch console logs in emulator / simulator use

   ionic emulate -l -c <PLATFORM>

2. If you wan't to watch console logs when testing in device you can launch this command :

   ionic run -l -c <PLATFORM>

-c = --consolelogs : Print app console logs to Ionic CLI (livereload req.)

-l = --livereload : Live reload app dev files from the device

May help someone !