title: Cannot set property 'name' of undefined JS
body: <p>I'm trying to understand JavaScript prototype and when I attempted coding this I get an error:</p>
  
  <pre><code>function Person(firstname, last name) {
    this.firstname = firstname;
    this.lastname = lastname;
  }
  
  var A = new Person('John', 'Doe');
  
  A.prototype.name = 'Toby';
  </code></pre>
  
  <p>I get an error stating cannot set property 'name' of undefined. Can't i assign a property on it's prototype of Object A. This is just a simple exercise to get an understanding of prototypes  </p>