问如何判断多姆重复何时完成冲压元素？

EN

<dom-module id="change-tester">
    <template>
    <h1>Change Tester</h1>
        <ul>
        <template id="template" is="dom-repeat" items="{{content}}">
            <li>{{item}}</li>
        </template>
        </ul>
        <button on-click="more">Add more</button>
    </template>
</dom-module>
<script>
    Polymer({

        is: 'change-tester',
        properties: {
            content: {
                type: Array,
                value: function(){ return ["one", "two", "three"]}
            }
        },
        ready: function(){
            this.$.template.addEventListener("dom-change", function(event){
               console.log(event);
            });
        },

        more: function(){
            this.push("content", "four");
            this.push("content", "five");
        }
    });
</script>

this.$$('#id')

this.shadowRoot.getElementById('id');

this.$$('#template')

ready: function(){
    this.$$('#template').addEventListener("dom-change", function(event){
        console.log(event);
    });
},