myClass.es6

class MyClass
{
  constructor(name) {
    this.name = name;
  }
  
  printName() {
    console.log(this.name);
  }
}

var myObject = new MyClass('bob');
myObject.printName();

myClass.js

function MyClass(name) {
  this.name = name;
}

MyClass.prototype.printName = function printName() {
  console.log(this.name);
}

var myObject = new MyClass('bob');
myObject.printName();

thanks man, I think that's a clear point now.