如何让频带在Chart.js中实现频带扩展？

var data = {
  labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
  datasets: [{
    label: 'Dataset',
    data: [10, 20, 30, 40, 50, 60, 70],
    backgroundColor: 'rgba(0, 0, 0, 0.1)',
    borderColor: 'rgba(0, 0, 0, 0.5)',
    borderWidth: 1
  }]
};

var options = {
  scales: {
    y: {
      beginAtZero: true
    }
  },
  plugins: {
    bands: {
      band1: {
        from: 20,
        to: 40,
        color: 'rgba(255, 0, 0, 0.2)'
      },
      band2: {
        from: 50,
        to: 70,
        color: 'rgba(0, 255, 0, 0.2)'
      }
    }
  }
};

var ctx = document.getElementById('myChart').getContext('2d');
var myChart = new Chart(ctx, {
  type: 'line',
  data: data,
  options: options
});

<canvas id="myChart"></canvas>