app.js

var Item = Vue.extend({
    data: function () {
        return {
          id: 0,
          message: ''
        };
    },
    template: '<li :data-id="id">{{ message }}</li>'
});

var demo = new Vue({
    el: '#demo',
    data: {
        title: 'items',
        items: []
    },
    mounted: function () {
    		Vue.nextTick(() => {
            var start = 0;
            var now = 0;
            setInterval(() => {
              now += 1;
              var item;
              var diff = 0;

              if (this.items.length > 15) {
     						  diff = this.items.length - 15;
                  var clone = this.$refs.wrapper.children[0].cloneNode(true);
                  for (var i = 0; i < diff; i++) {
                    var child = clone.removeChild(clone.children[0]);
                    child.textContent = now;
                    clone.appendChild(child);
                  }
                  console.log(clone);
                  this.$refs.wrapper.replaceChild(clone, this.$refs.wrapper.children[0]);
              } else {
                  var li = document.createElement('li');
                  li.textContent = now;
              		this.$refs.wrapper.children[0].appendChild(li);
                  this.items.push(now);
              }
            }, 1000);
        }); 
    }
})

template.html

<div id="demo" v-cloak>
    <div ref="wrapper">
        <ul>
        </ul>
    </div>
</div>