car.js

'use strict';

class Car {
  constructor(year, make, model, convertible) {
    this.year = year;
    this.make = make;
    this.model = model;
    // default parameters, much?
    if (typeof convertible === 'undefined') {
      this.convertible = false;
    } else {
      this.convertible = convertible;
    }
    this.speed = 0;
  }

  accelerate(delta) {
    this.speed += Math.abs(delta);
  }

  decelerate(delta) {
    this.speed -= Math.abs(delta);
  }

  convertibleString () {
    return this.convertible ? 'is' : 'is not';
  }

  toString () {
    return `This ${this.year} ${this.make} ${this.model}, which ${this.convertibleString()} a convertible, is travelling at ${this.speed}mph`;
  }
}

module.exports = new Car(2016, 'BMW', 'M6');

drive.js

const car = require('./car.js');

// going nowhere fast
console.log(car.toString());

// not quite topped out, but definite illegal in the US
car.accelerate(200);
console.log(car.toString());

// slightly more reasonable
car.decelerate(120);
console.log(car.toString());

// I'd like to see this shit in reality
car.convertible = true;
console.log(car.toString());

gistfile1.txt

This 2016 BMW M6, which is not a convertible, is travelling at 0mph
This 2016 BMW M6, which is not a convertible, is travelling at 200mph
This 2016 BMW M6, which is not a convertible, is travelling at 80mph
This 2016 BMW M6, which is a convertible, is travelling at 80mph