app.js

function svg2png(svgContent, width, height, callback) {
  // svgContent should be in base64
  let svgData = svgContent;
  let canvas = document.createElement("canvas");
  let context = canvas.getContext("2d");

  canvas.width = width;
  canvas.height = height;

  let image = new Image();
  image.onload = function () {
    // clear canvas
    context.clearRect(0, 0, width, height);
    // draw image with SVG data to canvas
    context.drawImage(image, 0, 0, width, height);
    // snapshot canvas as png
    let pngData = canvas.toDataURL("image/png");
    // pass png data URL to callback
    callback(pngData);
  };
  // start loading SVG data into in memory image
  image.src = svgData;
}

function downloadSVG(event, id) {
  let image = document.getElementById(id);
  svg2png(image.getAttribute("src"), 300, 300, function (data) {
    let a = document.createElement("a");
    a.download = `${image.dataset.uid}.png`;
    a.href = data;
    a.click();
  });
}