binding-inside.js

function Test(){

  this.element = document.querySelector(".hello");
  this.helloWorld();
    
}

Test.prototype.helloWorld = function(){

  var that = this;

  this.element addEventListener("click", function(e){ that.whatDidItGet(e) });
  // this is helloWorld
  
  this.element.addEventListener("click", that.whatDidItGet);
  // this is addEventListener
  
  this.element.addEventListener("click", (function(e){ this.whatDidItGet(e) }).bind(this));
  // this is helloWorld
  
  this.element.addEventListener("click", (that.whatDidItGet).bind(this));
  // this is helloWorld

};

Test.prototype.whatDidItGet = function(secret){

  console.log(secret);

};


new Test();