title: 'var' vs 'this' vs constructor-parameter variables
body: <p>In javascript given this three constructor functions:</p>
  
  <pre><code>function Foo(data) {
  
    var _data = data;
  
  }
  
  function Bar(data) {
  
    this.data = data;
  
  }
  
  function Baz(data) {
  
     //just use data freely.
  
  }
  </code></pre>
  
  <p>Is there any difference aside from the visibility of the <code>data</code> member after construction ? (e.g. you can do new <code>Bar().data</code> but not <code>new Foo().data</code>)</p>