title: data-bind with keyup event does not trigger
body: <p>I have a text input element that I want user to enter city or zip code and I want to trigger a javascript function as the user types text. My html is as follows</p>
  
  <pre><code>       &lt;input type="text"
          placeholder="Zip Code Or City Name"
          class="input-block-level"
          data-bind="value: searchterm, valueUpdate: 'afterkeydown', event: { keyup: getZipCodes }" /&gt;
  </code></pre>
  
  <p>in my viewmodel I have </p>
  
  <pre><code>var getZipCodes = function () {
          if (searchterm().length &lt; 2) {
              return;
          }
  
          datacontext.getZips(searchterm(), zipcodes);
          return true;
      };
  </code></pre>
  
  <p>But it turns out that the getZipCodes is never invoked.</p>
  
  <p>I tried data-binding to "onkeyup" but no go, I am sure there is some subtle error I am making. Can someone help me find what I am doing wrong?</p>
  
  <p>I tried changing getZipCodes to getZipCodes = function(data, event) {...} but that does not work either. The function just does not get invoked.</p>
  
  <p>By the way I am trying to do pretty much same as <a href="https://stackoverflow.com/questions/16120356/knockout-event-binding-for-input-keypress-causes-weird-behavior">Knockout event binding for input keypress causes weird behavior</a> </p>
  
  <p>but does not work for me.</p>