How this is dynamically bind to DOM elements.

listeners.js

// Suppose you have an html like:
// <div id="like-button">
//   <i class"icon-hand" />
//   <div>Like</div>
// </div>

function LikeButton(id) {
  this.buttonId = id;
  this.subscribe = function() {
    let btn = document.getElementById(this.buttonId);
    btn.addEventListener('click', function() {
      console.log(this); // Points to the event.target
    });
  }
}

let btn = new LikeButton('like-button');