If a user clicks on a form submit button and the page response is slow, the user may often re-click that button. Because the original request has already been submitted, you may find that the user has made a double submission. In e-commerce sites, the double submission of a credit card payment may be very unpopular with your customers. This is a common problem faced by web developers, and there are a variety of ways to try to prevent it. However, I have not seen a really elegant way to solve the problem, so I set about trying to find a simple and effective solution.