Can not see the plot in browser using the demo code

[honghh2018]

Hi developer,
when i use the below code to test the canvas2pdf.js , it show me the blank in web not the red rect.

<script src="/api/static/web/js/canvas2svg.js"></script>

  //make a mock canvas context using canvas2svg. We use a C2S namespace for less typing:

var ctx = new C2S(500,500); //width, height of your desired svg file
//do your normal canvas stuff:
ctx.fillStyle="red";
ctx.fillRect(100,100,100,100);
//ok lets serialize to SVG:
var myRectangle = ctx.getSerializedSvg(true); //true here will replace any named entities with numbered ones.
//Standalone SVG doesn't support most named entities.

Is anything wrong for this code?

Best,
hanhuihong