从Angular 4完全销毁ngDestroy方法中的图表

import { Component, OnInit, OnDestroy } from '@angular/core';
import * as Chart from 'chart.js';

@Component({
  selector: 'app-chart',
  template: '<canvas id="myChart"></canvas>',
})
export class ChartComponent implements OnInit, OnDestroy {
  private chart: Chart;

  ngOnInit() {
    const ctx = document.getElementById('myChart') as HTMLCanvasElement;
    this.chart = new Chart(ctx, {
      type: 'bar',
      data: {
        labels: ['Red', 'Blue', 'Yellow', 'Green', 'Purple', 'Orange'],
        datasets: [{
          label: '# of Votes',
          data: [12, 19, 3, 5, 2, 3],
          backgroundColor: [
            'rgba(255, 99, 132, 0.2)',
            'rgba(54, 162, 235, 0.2)',
            'rgba(255, 206, 86, 0.2)',
            'rgba(75, 192, 192, 0.2)',
            'rgba(153, 102, 255, 0.2)',
            'rgba(255, 159, 64, 0.2)'
          ],
          borderColor: [
            'rgba(255,99,132,1)',
            'rgba(54, 162, 235, 1)',
            'rgba(255, 206, 86, 1)',
            'rgba(75, 192, 192, 1)',
            'rgba(153, 102, 255, 1)',
            'rgba(255, 159, 64, 1)'
          ],
          borderWidth: 1
        }]
      },
      options: {
        scales: {
          y: {
            beginAtZero: true
          }
        }
      }
    });
  }

  ngOnDestroy() {
    if (this.chart) {
      this.chart.destroy();
    }
  }
}