...
export class Playground extends React.Component {
  chartRef: React.RefObject<Chart> = React.createRef();
  onSnapshot = () => {
    if (!this.chartRef.current) {
      return;
    }
    const snapshot = this.chartRef.current.getPNGSnapshot({
// can specify a background color or default is transparent
      backgroundColor: 'white',
      pixelRatio: 2,
    });
    if (!snapshot) {
      return;
    }
    const fileName = 'chart.png';
    switch (snapshot.browser) {
      case 'IE11':
        return navigator.msSaveBlob(snapshot.blobOrDataUrl, fileName);
      default:
        const link = document.createElement('a');
        link.download = fileName;
        link.href = snapshot.blobOrDataUrl;
        document.body.appendChild(link);
        link.click();
        document.body.removeChild(link);
    }
  };
...