Yes, I'm calling this lame, consider that a warning. About a year or so ago I migrated ColdFusion Cookbook to a static site using HarpJS. While doing this conversion, I changed my URL for entries from:

/entry/XX/NNNN (where XX is a database primary key and NNNN is a URL friendly text version of the title)

to

/entries/NNNN (where NNNN is the URL friendly text version of the title)

Unfortunately, I could not create a redirect for this because Amazon S3 only supports static redirects and maxes out at 50. You can't use a regex at all with their system. I kinda figured Google would take care of (and from what I can see, searches definitely turn up the right URLs) but this doesn't handle existing links. A reader emailed me about just that issue yesterday. I told him what I said here - I couldn't really do anything about it^* but I wondered if I could write some simple JavaScript code to attempt to help out with this.

I added the following code snippet to my 404 page:

document.addEventListener("DOMContentLoaded", function(){
	var path = window.location.pathname;
	if(path.indexOf("/entry/") === 0) {
		var parts = path.split("/");
		//why 4? cuz first part is blank
		if(parts.length === 4) {
			var intro = document.querySelector("#intro");
			var next = intro.nextSibling;
			var newUrl = "http://www.coldfusioncookbook.com/entries/" + parts[3] +".html";
			var p = document.createElement("p");
			p.innerHTML = "
The URL you attempted to load may possibly be found here: "+newUrl+".
";
			intro.parentNode.insertBefore(p, next);
		}
	} 
},false);

Taking it piece by piece, I begin by checking the current URL location, specifically the pathname. If I see /entry in the request, I then split it and count the pieces. My old URL syntax should return four pieces, and if so, I assume it is of the old format. I could be more anal here and check the second part to see if it is a number, but that felt like overkill.

I then simply generate a new URL and append it to the 404 page as a suggestion. I specifically decided against auto-redirecting as I thought the 'flash' of the 404 page would be annoying and seem like a bug. My code could also check to see if document.querySelector actually exists, or even simpler, use document.getElementById.

You can see an example of this here: http://www.coldfusioncookbook.com/entry/53/How-do-I-determine-if-a-number-is-even-or-odd.

As I said, this is lame, but I figure it is better than nothing. I wish S3 would support regex URLs, but for the price I pay (I'm averaging about 4 cents a month for my static sites there) I really can't complain.