Nice hint! In my case, I'm interested in the onload to be triggered only once; I have a one-time onload() for an image. After that, I make a drawImage with the already loaded image.

Drawback: in case the original image changed but keeps the URL, the image will be drawn from browser cache... If I make this Date() trick, I will unnecessarily load the browser cache with identical images.

Nevertheless I think it's good to implement it with the Date() trick.