帶註釋的監聽器

新增事件偵聽器的另一種方法是在 DOM 中使用 on-event 註釋。下面是使用 up 事件的示例，當手指/滑鼠上升時會觸發該事件

<dom-module id="annotated-listener">
  <template>
    <style>
      .inner{
        width: calc(200px);
        height: 50px;
        border: 1px solid blue;
        margin-top: 15px;
      }
    </style>
    <!-- As up is the name of the event annotation will be on-up -->
    <div class="inner" on-up='upEventOccurs'>Tap me for different alert</div>
  </template>
</dom-module>
<script>
  Polymer({
    is:'annotated-listener',
    upEventOccurs:function(e){
      //detail Object in event contains x and y co-ordinate of event
      alert('up event occurs at x:'+e.detail.x+' y:'+e.detail.y);
    }
  })
</script>