如何对VueJs中的值求和

new Vue({
  data: {
    numbers: [1, 2, 3, 4, 5]
  }
});

<div>
  <span v-for="number in numbers" v-bind:key="number">{{ number }}</span>
</div>

new Vue({
  data: {
    numbers: [1, 2, 3, 4, 5]
  },
  computed: {
    sum: function() {
      return this.numbers.reduce(function(total, number) {
        return total + number;
      }, 0);
    }
  }
});

<div>
  <span v-for="number in numbers" v-bind:key="number">{{ number }}</span>
  <p>Sum: {{ sum }}</p>
</div>