title: add a binding (e.g. hasfocus) to specific item in observable array dynamically
body: <p>I'm using knockoutJS to handle an editable list of website name and URL pairs in a table - there's a button underneath to add a new item. My code is based on the <a href="http://learn.knockoutjs.com/#/?tutorial=collections" rel="nofollow">lists and collections tutorial</a>.</p>
  
  <pre><code>....
  &lt;tbody data-bind="foreach: website"&gt;
   &lt;tr&gt;
    &lt;td&gt;&lt;input data-bind="value: name, hasfocus: true" /&gt;&lt;/td&gt;
    &lt;td&gt;&lt;input data-bind="value: url" /&gt;&lt;/td&gt;
    &lt;td&gt;&lt;a href="#" data-bind="click: $root.removeWebsite"&gt;Remove&lt;/a&gt;&lt;/td&gt;
   &lt;/tr&gt;
  &lt;/tbody&gt;
  &lt;/table&gt;
  
  &lt;button data-bind="click: addWebsite" class="btn"&gt;Add another&lt;/button&gt;
  </code></pre>
  
  <p>Note I use <code>hasfocus: true</code> so that each time a new blank field is added they don't have to click it with the mouse.   You'll also see in the code below (from the viewmodel function) that I'm checking the contents of the last text box in the list before I allow people to add another one. </p>
  
  <pre><code>// Add and remove
  self.addWebsite = function() {
  
      var length = self.website().length;
      if (self.website()[length - 1].name == '') {
          // Last site in list has no name, don't allow them to add another
          return false;
      }
  
      self.website.push(new dashboardApp.website());
  }
  </code></pre>
  
  <p>Is there a way of changing the binding during runtime - so I can give the last item focus as a prompt to the user that they should be filling it in rather than creating further blank rows, e.g. something like:</p>
  
  <pre><code>self.website()[length - 1].name.hasfocus = true;
  </code></pre>