title: drawImage (canvas) is not working
body: <p>I want to draw multiple canvases on a single canvas using <code>drawImage()</code> method but it is not working 
  <strong>Code</strong></p>
  
  <pre><code>&lt;html&gt;
   &lt;head&gt;
    &lt;script&gt;
      window.onload = function() {
      var context1= document.getElementById("canvas1").getContext("2d");
      var context2  = document.getElementById("canvas2").getContext("2d");
      var context3  = document.getElementById("canvas3").getContext("2d");
  
      context1.font = "20pt Calibri";
      context1.fillStyle = "blue";
      context1.fillText("Hello ", 50, 25);
  
      context2.font = "20pt Calibri";
      context2.fillStyle = "red";
      context2.fillText("World!", 100, 25);
  
      var imageObj = new Image();
       imageObj.onload = function() {
        context3.drawImage(context1.canvas, 50, 25);
        context3.drawImage(context2.canvas, 100, 25);
          };
    };
  
  &lt;/script&gt;
   &lt;/head&gt;
  &lt;body&gt;
  &lt;canvas id="canvas1" class="canvas" width="200" height="50"&gt;&lt;/canvas&gt;
  &lt;canvas id="canvas2" class="canvas" width="200" height="50"&gt;&lt;/canvas&gt;
  &lt;canvas id="canvas3" class="canvas" width="200" height="50"&gt;&lt;/canvas&gt;
  &lt;/body&gt;
  &lt;/html&gt;​
  </code></pre>
  
  <p><strong>JS Fiddle</strong>
  <a href="http://jsfiddle.net/4xT2j/2/" rel="nofollow">http://jsfiddle.net/4xT2j/2/</a></p>