title: javascript inheritance and instance variables
body: <p>I'm trying to understand how inheritance works in JS. Suppose we have a class:</p>
  
  <pre><code>Class = function () {
      this.A = 'A';
      this.B = 'B';
  };
  </code></pre>
  
  <p>and we are trying to extend it</p>
  
  <pre><code>SubClass = function () {};
  SubClass.prototype = new Class();
  </code></pre>
  
  <p>Do I understance correctly that after inheritance properties <code>A</code> and <code>B</code> are common for all instances of <code>SubClass</code>, since they belong to it's prototype? If yes, how can <code>Class</code> be extended so that <code>A</code> and <code>B</code> do not be part of prototype?</p>
  
  <p><strong>UPD:</strong> note that <code>Class</code> uses <code>A</code> and <code>B</code>, so I can't declare them in SubClass.</p>
  
  <p>Thank you in advance!</p>