Vue.js - updated array item value doesn't update in page

This is due to the array change caveats.

Do it like this instead

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]);
    }
  }
});

Here is thefiddle