title: knockout.js variable update on attr change
body: <p>I've got a jQuery UI slider. When the user uses a slider, the slider updates an attr variable in the div tag of the slider </p>
  
  <pre><code>$(".slider").each(function() {
  var value = parseInt($(this).attr('data-init-value'), 10);
  var amin = parseInt($(this).attr('data-min'), 10);
  var amax = parseInt($(this).attr('data-max'), 10);
  console.log(value, " ", amin, " ", amax)
  $(this).empty().slider({
      value : value,
      min : amin,
      max : amax,
      range : "min",
      animate : true,
      slide : function(event, ui) {
          $(this).attr('data-value', ui.value);
      }
  });
  </code></pre>
  
  <p>});</p>
  
  <p>The example div tag in the html:</p>
  
  <pre><code>&lt;div class="slider" data-min="200" data-max="600" data-init-value="300" data-bind="attr: { 'data-value': someValue }"&gt;&lt;/div&gt;
  </code></pre>
  
  <p>When the slider is changed the  data-value is updated in the <code>&lt;div&gt;</code> but the js variable doesn't change. (in other, trivial binding cases - like text: - it works.)</p>
  
  <p>How to bind this action?</p>