2.js

<canvas id="canvas"></canvas>
<script type="text/javascript">
var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');
Image img1 = new Image();
Image img2 = new Image();

img1.onload = function() {
    canvas.width = img1.width;
    canvas.height = img1.height;
    img2.src = 'imgfile2.png';
};
img2.onload = function() {
    context.drawImage(img1, 0, 0);
    context.drawImage(img2, 0, 0);
};        

img1.src = 'imgfile1.png';
</script>