将svg转为png，jpg等图片类型。

const image = new Image();
// image.src =
//   'data:image/svg+xml;base64,' +
//   window.btoa(unescape(encodeURIComponent(svg)));
image.src = './xxx.svg';
image.onload = function () {
  var canvas = document.createElement('canvas');
  canvas.width = 6400;
  canvas.height = 3400;
  var context = canvas.getContext('2d');
  context.drawImage(image, 0, 0);
  var a = document.createElement('a');
  a.href = canvas.toDataURL('image/png', 1);
  a.download = 'xxx.png';
  a.click();
};