title: constructor function not showing correct results
body: <p>i am a newbie here.
  i am trying to create a car object and instances.
  The code is</p>
  
  <pre><code>  function Car(name, speed) {
          this.name = name;
          this.speed = speed;
          this.describe=describeCar;
      };
  
  
      function describeCar(){
          document.write("The Full name is " + this.name + " and the top speed is " + this.speed);
      };
  
      var mercedes = new Car("Mercedes benz", 233); // Instance of Object
      var bmw = new Car("British motor Works", 260); // Instance of Object
      mercedes.describeCar();
  </code></pre>
  
  <p>Now i don't see anything in browser.
  please tell me what i am doing wrong.
  Thanks so much!.</p>