Vue Chart.js - Chart is not updating when data is changing

I'm using Vue.js and Chart.js to draw some charts. Each time I call the function generateChart(), the chart is not updated automatically. When I check the data in Vue Devtools, they are correct but the chart does not reflect the data. However, the chart does update when I resize the window.

What is wrong with what I'm doing?
How do I update the chart each time I call generateChart() ?

I feel this is going to be something related with object and array change detection caveats, but I'm not sure what to do.

https://codepen.io/anon/pen/bWRVKB?editors=1010

<template>
    <el-dialog title="Chart" v-model="showGeneratedChart">
        <line-chart :chartData="dataChart"></line-chart>
    </el-dialog>
</template>

<script>
export default {
    data() {
        const self = this;
        return {
            dataChart: {
                labels: [],
                datasets: [
                    {
                        label: "label",
                        backgroundColor: "#FC2525",
                        data: [0, 1, 2, 3, 4],
                    },
                ],
            },
        };
    },
    methods: {
        generateChart() {
            this.dataChart["labels"] = [];
            this.dataChart["datasets"] = [];

            // ... compute datasets and formattedLabels

            this.dataChart["labels"] = formattedLabels;
            this.dataChart["datasets"] = datasets;
        },
    },
};
</script>

LineChart.js

import { Line, mixins } from 'vue-chartjs'

export default Line.extend({
    mixins: [mixins.reactiveProp],
    props: ["options"],
    mounted () {
        this.renderChart(this.chartData, this.options)
    }
})

Solution

Use a computed property for the chart data. And instead of calling this.renderChart on watch wrap it in a method and reuse that method on mounted and in watch.

Vue.component("line-chart", {
  extends: VueChartJs.Line,
  props: ["data", "options"],
  mounted() {
    this.renderLineChart();
  },
  computed: {
    chartData: function() {
      return this.data;
    }
  },
  methods: {
    renderLineChart: function() {
    this.renderChart(
      {
        labels: [
          "January",
          "February",
          "March",
          "April",
          "May",
          "June",
          "July"
        ],
        datasets: [
          {
            label: "Data One",
            backgroundColor: "#f87979",
            data: this.chartData
          }
        ]
      },
      { responsive: true, maintainAspectRatio: false }
    );      
    }
  },
  watch: {
    data: function() {
      this._chart.destroy();
      //this.renderChart(this.data, this.options);
      this.renderLineChart();
    }
  }
});

var vm = new Vue({
  el: ".app",
  data: {
    message: "Hello World",
    dataChart: [10, 39, 10, 40, 39, 0, 0],
    test: [4, 4, 4, 4, 4, 4]
  },
  methods: {
    changeData: function() {
      this.dataChart = [6, 6, 3, 5, 5, 6];
    }
  }
});

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>Vue.jS Chart</title>
</head>
<body>
<div class="app">
    {{ dataChart }}
   <button v-on:click="changeData">Change data</button>
  <line-chart :data="dataChart" :options="{responsive: true, maintainAspectRatio: false}"></line-chart>
 
</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.2.6/vue.min.js"></script>
<script src="https://unpkg.com/vue-chartjs@2.5.7-rc3/dist/vue-chartjs.full.min.js"></script>
</body>
</html>

You could also make the options a computed property, and if option not going to change much you can setup default props. https://v2.vuejs.org/v2/guide/components.html#Prop-Validation

Here is a working codepen https://codepen.io/azs06/pen/KmqyaN?editors=1010