title: How to check if a knockout observable exists?
body: <p>Say I have a json of observables :</p>
  
  <pre><code>self.name = ko.observable('Arnab');
  self.surname= ko.observale('Bhagabati')
  
  var person = {
    name:ko.observable('Arnab'),
    lastName= ko.observale('Bhagabati')
  }
  </code></pre>
  
  <p>I can access the name of person by <code>console.log(person.name());</code>
  <br><br>How do I check whether my <code>person</code> has a knockout observable property called, say <code>salary</code>?</p>
  
  <pre><code>if (typeof person.salary() !== 'undefined')
  </code></pre>
  
  <p>gives <code>params.salary is not a function</code> </p>