application.js

export default class Application {

    constructor(container) {

        this[container] = container;

    }

    init() {

        this.startSequence();

    }

    startSequence() {

        console.log(this[container]);

    }

    stopSequence() {

        console.log('Stopped!');

    }

}

let container = document.getElementById('app');
let ToDo = new Application(container);

ToDo.init();