How can multiple Imported classes call each others methods?

I have this index.js file:

import GameController from './Controllers/GameController'
import LandController from './Controllers/LandController'

const GAME = new GameController();
const LAND = new LandController();

And in this class, I want to call a function every second using setInterval:

export default class GameController {
  tickCount = 0;

  tick = setInterval( () => {
    this.Tick()
  }, 1000);

  Tick () {
    LAND.updateLand();
    this.tickCount++;
  }

}

But I get this error:

Uncaught ReferenceError: GAME is not defined

I'm new to webpack, I had this working in vanilla javascript but I'm still learning, so any help would be greatly appreciated! Thank you

EDIT: Updated GameController class based on bravo's answer, however now I get the error:

Uncaught ReferenceError: LAND is not defined

How can I make it so multiple classes can call each others methods?

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