title: Watch for variable change do not work
body: <p>I need to check variable <code>rasters_previews_list</code> for changing. Here is my code:</p>
  
  <pre><code>var userContent = Vue.extend({
    template: '&lt;p&gt;Some template&lt;/p&gt;',
    data: function ()  {
      return {
        rasters_previews_list: []
      }
    },
    watch: {
      'rasters_previews_list': function(value, mutation) {
        console.log("Value changed");      
      }
    }
  });
  </code></pre>
  
  <p>But In console I do not see <code>Value changed</code> when it got new data.</p>
  
  <p>Data changing function:</p>
  
  <pre><code>map.on('draw:created', function (e) {
  //...
  
     Vue.http.post('/dbdata', DataBody).then((response) =&gt; {
        userContent.rasters_previews_list = response; // putting JSON answer to Component data in userContent
  
        console.log(response);
  
  
        }, (response) =&gt; {
            console.log("Can't get list rasters metadata from DB. Server error: ", response.status)
        });
  </code></pre>
  
  <p>I change value in <code>map.on('draw:created', function (e)</code> (Leaflet JS). I see console.log output, so seems data is changing.</p>