JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://unpkg.com/vue"></script>
<script src="https://cdn.jsdelivr.net/vue.resource/1.3.1/vue-resource.min.js"></script>
<section id="content">
  <div>Value in array: {{ test[0].array[0] }}</div>
  <div>Value in number: {{ number }}</div>
<button @click="setArray">change</button>
</section>

JavaScript

var vue = new Vue({
  el: '#content',

  data: {
    test: [{
      array: [0, 0, 0, 0]
    }, {
      array: [0, 0, 0, 0]
    }],
    number: 0
  },

  methods: {
    setNumber: function() {
      this.number = 5;
      console.log(this.number);
    },
    setArray: function() {
      //this.test[0].array[0] = 9;
	  this.$set(this.test[0].array, 0, 9);
      console.log(this.test[0].array[0]);
    }
  }
});