title: knockout selected option binding
body: <p>I want to bind the selected option to a dropwdown in html
  but if i changed the model value using the select option automatically the variable changed to object than string</p>
  
  <pre><code>&lt;select data-bind="options: Types, selectedOptions: chosenType"&gt;&lt;/select&gt;
  
      self.Types = ['xxx', 'yyy', 'zzzz'];
  
      self.chosenType = ko.observable('xxx');
  </code></pre>
  
  <p>if i changed the value from xxx to yyy using dropdown the chosenType = ['yyy'] where i want to be just a string 'yyy', where i should access the value as chosenType[0]
  but service accepts just a string value.
  please help me with this</p>