title: get the expression value in ng-model
body: <p>My code is</p>
  
  <pre><code>&lt;input type="text"  class="form-control" name="tot" ng-model="myModel.tot"
   ng-init="myModel.tot = {{myModel.date1 | amDifference : myModel.date2 :'years'}} years"  
   required="required"/&gt;
  </code></pre>
  
  <p>If {{myModel.date1 | amDifference : myModel.date2 :'years'}} years = 3 years, I need myModel.tot= 3 years. But am not getting it.</p>
  
  <p>Please help me to get the value. </p>