Multiple Canvas Elements to PDF using jsPDF

HTML

<script src="https://mrrio.github.io/jsPDF/dist/jspdf.debug.js"></script>
<script src="https://html2canvas.hertzen.com/build/html2canvas.js"></script>
<canvas id="canvas" width="480" height="320"></canvas>
<canvas id="canvas2" width="480" height="320"></canvas>
<button id="download">Download Pdf</button>

CSS

#canvas {}

#background {
  display: none;
}

#ballon {
  position: absolute;
  top: 50px;
  left: 50px;
  cursor: move;
  opacity: 0.5;
}

JavaScript

$(document).ready(function() {
  var d_canvas = document.getElementById('canvas');
  var context = d_canvas.getContext('2d');
  context.moveTo(20, 20);
  context.lineTo(100, 20);
  context.fillStyle = "#999";
  context.beginPath();
  context.arc(100, 100, 75, 0, 2 * Math.PI);
  context.fill();
  context.fillStyle = "orange";
  context.fillRect(20, 20, 50, 50);
  context.font = "24px Helvetica";
  context.fillStyle = "#000";
  context.fillText("Canvas", 50, 130);

  var d_canvas2 = document.getElementById('canvas2');
  var context2 = d_canvas2.getContext('2d');
  context2.moveTo(20, 20);
  context2.lineTo(100, 20);
  context2.fillStyle = "#999";
  context2.beginPath();
  context2.arc(100, 100, 75, 0, 2 * Math.PI);
  context2.fill();
  context2.fillStyle = "orange";
  context2.fillRect(20, 20, 50, 50);
  context2.font = "24px Helvetica";
  context2.fillStyle = "#000";
  context2.fillText("Canvas", 50, 130);

  $('#download').click(function() {
    //create a canvas
    canvas3 = document.createElement('canvas');
    canvas3.id = 'canvas3'
    document.body.appendChild(canvas3);
    canvas3.width = 500;
    canvas3.height = 500;

    //add the images
    base_image = new Image();
    context3 = canvas3.getContext('2d');
    context3.drawImage(d_canvas,0,0);
    context3.drawImage(d_canvas2,0,200);

    var doc = new jsPDF('p', 'mm');
    html2canvas($("#canvas3"), {
      onrendered: function(canvas) {
        var imgData = canvas.toDataURL(
          'image/png');
        doc.addImage(imgData, 'PNG', 10, 10);
        doc.save('sample-file.pdf');
      }
    });
  });
});