Untitled

<!DOCTYPE html>
<html>
  <body>

    <canvas id="myCanvas" width="600" height="600" style="border:1px solid #d3d3d3;">
      Your browser does not support the HTML5 canvas tag.</canvas>

    <script>
      var c = document.getElementById("myCanvas");
      var ctx = c.getContext("2d");

      var w = 600;
      var h = 600;
      var data = ctx.createImageData(w, h);
      for (var i = 0; i < w*h; i++) {
			  data.data[4*i+3] = 255;
			  }
			  for (var i = 0; i < Math.min(w, h); i++) {
					      data.data[4*i*(i+1)+0] = 255;
					      data.data[4*i*(i+1)+0] = 255;


					      }
					      ctx.putImageData(data, 0, 0);
					      </script>

  </body>
</html>