car.js

// Run: `node --harmony car.js`

"use strict";

var Car = function(brand) {

  this.brand = brand;

  this.vroom = function() {
    console.log(this.brand + " is slow");
    return new Promise(function(f) {
      console.log(this.brand + " is slow"); f("vroom");
    }.bind(this));
  };

  this.vrooom = () => {
    console.log(this.brand + " is fast");
    return new Promise((f) => {
      console.log(this.brand + " is fast"); f("vrooom");
    });
  };

};

var c = new Car("Mazda");

c.vroom().then(function(r) { console.log('Promised: ' + r); }, function(e) { console.log('Broken: ' + e); });
c.vrooom().then(function(r) { console.log('Promised: ' + r); }, function(e) { console.log('Broken: ' + e); });

Expected:

Mazda is slow
Mazda is slow
Mazda is fast
Promised: vroom
Broken: TypeError: Cannot read property 'brand' of undefined

Desired:

Mazda is slow
Mazda is slow
Mazda is fast
Mazda is fast
Promised: vroom
Promised: vrooom