JavaScript: Ways to use `this` in callback function

this.js

// The old way (before ES6)
var _self = this;
this.element.addEventListener('click', function (event) {
  _self.doSomething(event);
});

// The new way (ES6)
this.element.addEventListener('click', (event) => {
  this.doSomething(event);
});

// The recommended way
this.element.addEventListener('click', this.doSomething.bind(this));