Dirty Tricks for Dirty Problems
Normally, with access to a server side language, this would be easy to implement. In .NET it could be checked with a single line of code using the System.IO.File class and its static Exists method.
However, in my case, the path to the image was generated by a tool and I couldn't modify it. All I had access to was the client HTML for the image, but I always got back a full image path to the product's image, whether it existed or not. The code just assumed that there would always be an image available named after its product ID (e.g. 12345.jpg).
I could of course create "No image available" images for all the missing images, but that would have meant a lot of work. Besides, it wasn't future-proof as it was quite likely new products without images would pop up in the system.
Then I remembered a little client side trick using the onerror attribute. All I needed to do was change the src attribute of the image in its onerror handler, like this:
<img src="http://imar.spaanjaars.com/DoesNotExist.jpg" onerror="this.onerror=null; this.src='http://imar.spaanjaars.com/DoesExist.jpg';" />
When the image cannot be loaded successfully, the img element fires its onerror event. Inside the (in-line) handler for that event, a new image is loaded that does exist.
Simple, and easy to implement. Note that this solution may not work in all browsers, as it's currently not standards compliant. It looks like it's going to be added to HTML 5 though (warning: this is a huge document).
Where to Next?
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