x-example.html

<dom-module id="x-example">
  <style>
    
    :host {
      display: block;
    }
        
  </style>
  <template>
     <div id="text">x-example</div>
  </template>
  <script>  
    Polymer({

      is: 'x-example',
      
      properties: {
        test: {
          type: String,
          value: '',
          observer: '_testChanged'
        }
      },

      _testChanged: function(newTest, oldTest) {
        console.log('_testChanged(', newTest, ',', oldTest, ')');
      }

    });
  </script>
</dom-module>