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HTML5 Canvas no method 'toDataURL'

My Code is like this

    <html>
  <head>
  </head>
  <body>
    <canvas id="myCanvas" width="578" height="200" style="display:none;"></canvas>
    <img id="canvasImg" onclick="myFunction()" alt="Right click to save me!">
    <script>
        var canvas = document.getElementById('myCanvas');
        var context = canvas.getContext('2d');
        function myFunction() {
            var c = document.getElementsByTagName("canvas");
            // save canvas image as data url (png format by default)
            var dataURL = c.toDataURL();
            // set canvasImg image src to dataURL
            // so it can be saved as an image
            document.getElementById('canvasImg').src = dataURL;
        }
    </script>
  </body>
</html> 

When i click on canvasImg its throwing an error

Uncaught TypeError: Object #<NodeList> has no method 'toDataURL' 

I have made a fiddle here Can any one point out whats going wrong?

DEMO

document.getElementsByTagName returns array of elements objects, and no array objects have method toDataUrl

instead of this

var c = document.getElementsByTagName("canvas"); 

use

 var c = document.getElementsByTagName("canvas")[0];
    function myFunction() {
         var canvas = document.getElementById("myCanvas");
         var context = canvas.getContext("2d");
         var img = document.getElementById("canvasImg");
         context.drawImage(img, 0, 0);
    }

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