HTML Canvas boilerplate

<!DOCTYPE HTML>
<html>
  <body>
    <canvas id="myCanvas" width="1000" height="1000"></canvas>
    <script>
      function drawImage() {
        var canvas = document.getElementById('myCanvas');
        var context = canvas.getContext('2d');
        var imageWidth = canvas.width = Math.min(canvas.width, window.innerWidth);
        var imageHeight = canvas.height = Math.min(canvas.height, window.innerHeight);
        var imageData = context.createImageData(imageWidth, imageHeight);
        
        // iterate over all pixels based on x and y coordinates
        for(var y = 0; y < imageHeight; y++) {
          // loop through each column
          for(var x = 0; x < imageWidth; x++) {
            imageData.data[(imageWidth*y + x) * 4 + 0] = y/imageHeight * 255;
            imageData.data[(imageWidth*y + x) * 4 + 1] = y/imageHeight * 255;
            imageData.data[(imageWidth*y + x) * 4 + 2] = x/imageWidth * 255;
            imageData.data[(imageWidth*y + x) * 4 + 3] = 255;
          }
        }
        context.putImageData(imageData, 0, 0); 
      }
      drawImage();
    </script>
  </body>
</html>