title: vue-resource: How is success of a $http request determined?
body: <p>In vue-resource, while making a call such as:</p>
  
  <pre><code> this.$http.post('/someUrl', formData).then(response =&gt; {
      // success callback
    }, response =&gt; {
      // error callback
    });
  </code></pre>
  
  <p>how is whether the success or failure callback will be executed chosen? Is it determined by some property of the response object?</p>