gistfile1.js

function Car() {
  this.speed = 0
}

Car.prototype.accelerate = function(by) {
  var self = this;

  
  function throttler() {
    if (by > 20) {
      self.speed += 20;
    } else {
      self.speed += by;
    }
  }
  
  throttler();
}

accord = new Car()
accord.accelerate(40);
console.log(accord.speed);