How to convert jpg image to png using javascript

If we have a look at the source from the JPG to PNG website which uses pure javascript to convert images from JPG to PNG. We see that they:

1. Load the jpg image from file
2. Create a canvas of the same size as the jpg
3. Draw the jpg image covering the whole canvas
4. Convert canvas to blob (if the image is small enough you can also use to .toDataURL())
5. Download the blob