How to save the contents of a div as a image?

Basically, I am doing what the heading states, attempting to save the contents of a div as an image.

I plan on making a small online application for the iPad.

One function that is a must is having a 'Save' button that can save the full webpage as an image, and save that image to the iPad's camera roll. I wish to save the full contents of a div, not just the visible area.

I have searched briefly online, but couldn't find much documentation on anything. I found a lot on HTML5 Canvas. Here is some code I put together:

<script>
function saveimg()
{
    var c = document.getElementById('mycanvas');
    var t = c.getContext('2d');
    window.location.href = image;

    window.open('', document.getElementById('mycanvas').toDataURL());
}
</script>

<div id="mycanvas">
This is just a test<br />
12344<br />
</div>

<button onclick="saveimg()">Save</button>

Although, I am getting this error:

TypeError: c.getContext is not a function

This application will be built only with HTML, CSS and jQuery (or other Javascript libraries).

There are several of this same question (1, 2). One way of doing it is using canvas. Here's a working solution. Here you can see some working examples of using this library.

Do something like this:

A <div> with ID of #imageDIV, another one with ID #download and a hidden <div> with ID #previewImage.

Include the latest version of jquery, and jspdf.debug.js from the jspdf CDN

Then add this script:

var element = $("#imageDIV"); // global variable
var getCanvas; // global variable
$('document').ready(function(){
  html2canvas(element, {
    onrendered: function (canvas) {
      $("#previewImage").append(canvas);
      getCanvas = canvas;
    }
  });
});
$("#download").on('click', function () {
  var imgageData = getCanvas.toDataURL("image/png");
  // Now browser starts downloading it instead of just showing it
  var newData = imageData.replace(/^data:image\/png/, "data:application/octet-stream");
  $("#download").attr("download", "image.png").attr("href", newData);
});

The div will be saved as a PNG on clicking the #download