How to queue ajax posted form data when connection is down

I have a kiosk web page that users use to sign in at an event.

On the page there is a form with a name and email input.

To prevent slow responses due to connection problems I have set up the ui to send asynchronous ajax posts.

The problem is that the connection may not be available, but I don't want to lose the data that was submitted (if the browser was accidentally closed for example). What is a way to go about saving the form data and auto retrying sending it when the connection is available?

Is this a paradigm that exists or would I have to write a full solution myself?

I was considering using HTML 5 persistent storage.

You could use evercookie or some of its ideas for storage