JavaScript 下載svg圖片為png格式

var doctype = '<?xml version="1.0" standalone="no"?><!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd" [<!ENTITY nbsp " ">]>'; 
function convertToPng(src, w, h) { 
 var canvas = document.createElement('canvas'); 
 var context = canvas.getContext('2d'); 
 canvas.width = w; 
 canvas.height = h; 
 context.drawImage(src, 0, 0); 
 var png; 
 try { 
 png = canvas.toDataURL("image/png"); 
 } catch (e) { 
 if ((typeof SecurityError !== 'undefined' && e instanceof SecurityError) || e.name == "SecurityError") { 
  console.error("Rendered SVG images cannot be downloaded in this browser."); 
  return; 
 } else { 
  throw e; 
 } 
 } 
 return png; 
 } 
 function isElement(obj) { 
 return obj instanceof HTMLElement || obj instanceof SVGElement; 
 } 
 function reEncode(data) { 
 data = encodeURIComponent(data); 
 data = data.replace(/%([0-9A-F]{2})/g, function (match, p1) { 
 var c = String.fromCharCode('0x' + p1); 
 return c === '%' ? '%25' : c; 
 }); 
 return decodeURIComponent(data); 
 } 
 function uriToBlob(uri) { 
 var byteString = window.atob(uri.split(',')[1]); 
 var mimeString = uri.split(',')[0].split(':')[1].split(';')[0] 
 var buffer = new ArrayBuffer(byteString.length); 
 var intArray = new Uint8Array(buffer); 
 for (var i = 0; i < byteString.length; i++) { 
 intArray[i] = byteString.charCodeAt(i); 
 } 
 return new Blob([buffer], {type: mimeString}); 
 } 
 function downLoad(el, name) { 
 if (!isElement(el)) { 
 throw new Error('an HTMLElement or SVGElement is required; got ' + el); 
 } 
 if (!name) { 
 console.error("文件名為空!"); 
 return; 
 } 
 var xmlns = "http://www.w3.org/2000/xmlns/"; 
 var clone = el.cloneNode(true); 
 clone.setAttribute("version", "1.1"); 
 if (!clone.getAttribute('xmlns')) { 
 clone.setAttributeNS(xmlns, "xmlns", "http://www.w3.org/2000/svg"); 
 } 
 if (!clone.getAttribute('xmlns:xlink')) { 
 clone.setAttributeNS(xmlns, "xmlns:xlink", "http://www.w3.org/1999/xlink"); 
 } 
 var svg = clone.outerHTML; 
 var uri = 'data:image/svg+xml;base64,' + window.btoa(reEncode(doctype + svg)); 
 var image = new Image(); 
 image.onload = function () { 
 var png = convertToPng(image, image.width, image.height); 
 var saveLink = document.createElement('a'); 
 var downloadSupported = 'download' in saveLink; 
 if (downloadSupported) { 
  saveLink.download = name + ".png"; 
  saveLink.style.display = 'none'; 
  document.body.appendChild(saveLink); 
  try { 
  var blob = uriToBlob(png); 
  var url = URL.createObjectURL(blob); 
  saveLink.href = url; 
  saveLink.onclick = function () { 
  requestAnimationFrame(function () { 
  URL.revokeObjectURL(url); 
  }) 
  }; 
  } catch (e) { 
  saveLink.href = uri; 
  } 
  saveLink.click(); 
  document.body.removeChild(saveLink); 
 } 
 }; 
 image.src = uri; 
 } 

<div id="svg-parent-div"><svg>...</svg></div> 

var el = d3.select("#svg-parent-div").node().children[0]; 
download(el,"下載圖片"); 

el.setAttributeNS(xmlns, "xmlns", "http://www.w3.org/2000/svg"); 
el.setAttributeNS(xmlns, "xmlns:xlink", "http://www.w3.org/1999/xlink");