title: Knockout attribute binding does not work with a custom function
body: <p>I have a knockout model which has a <code>bar</code> element inside and I have a custom function <code>foo()</code> which is not in the model and is used to format data.</p>
  
  <p>When I am binding the model to an html view with something like this:</p>
  
  <pre><code>&lt;span data-bind="text: foo(bar), attr: { 'title': foo(bar)}"&gt;&lt;/span&gt;
  </code></pre>
  
  <p>it works only partially: text is formatted, but attribute title is ignored (no error is risen, it is just ignored). But when I use:</p>
  
  <pre><code>&lt;span data-bind="text: foo(bar), attr: { 'title': bar}"&gt;&lt;/span&gt;
  </code></pre>
  
  <p>the title is output as a 'bar'. So basically custom functions are not working with attribute binding.</p>
  
  <p>So is there a way to make my <code>foo(bar)</code> work properly?</p>
  
  <p>P.S. here is a reproducible code:</p>
  
  <p><strong>HTML view</strong></p>
  
  <pre><code>&lt;span data-bind="foreach: listOfReports"&gt;
      &lt;div class="10"&gt;
          &lt;span data-bind="text: Helper.timestamp2HumanReadable(date), attr: { 'title': Helper.timestamp2Date(date)}"&gt;&lt;/span&gt;
      &lt;/div&gt;
  &lt;/span&gt;
  </code></pre>
  
  <p><strong>ViewModel</strong></p>
  
  <pre><code>function ArticlesViewModel() {
      this.listOfReports      = ko.observableArray([{'date' : 1283364108}, {'date' : 1893364108}]);
  };
  ko.applyBindings(new ArticlesViewModel());
  </code></pre>
  
  <p>and when I started to write my code to make it reproducible I saw that I am not returning a correct value in my function in Helper. </p>
  
  <p>Sorry all of you guys for this post and for wasting your time. I hope I will never do this next time. Thank you very much for help.</p>