如何将svg格式转换为png格式并保存到ie11中？

 if (xhr.readyState === 4 && xhr.status === 200) {

   var svgContent = xhr.responseText;

   var canvas = document.getElementById('canvas');

   var ctx = canvas.getContext('2d');

   var DOMURL = window.URL || window.webkitURL || window;

   var img = new Image();

   img.onload = function() {

     ctx.drawImage(img, 0, 0);

     var pngDataUrl = canvas.toDataURL('image/png');

     // 保存PNG图像到IE11中

     if (window.navigator.msSaveBlob) {

       var blob = dataURLtoBlob(pngDataUrl);

       window.navigator.msSaveBlob(blob, 'image.png');

     }

   };

   img.src = 'data:image/svg+xml,' + encodeURIComponent(svgContent);

 }

 var arr = dataURL.split(',');

 var mime = arr[0].match(/:(.*?);/)[1];

 var bstr = atob(arr[1]);

 var n = bstr.length;

 var u8arr = new Uint8Array(n);

 while (n--) {

   u8arr[n] = bstr.charCodeAt(n);

 }

 return new Blob([u8arr], { type: mime });