GoogleChrome/dialog-polyfill — pull request #25 by tehnomaag (2014-10-20 15:31:22+00:00)
Title: Added cancelable:true to the cancel event.

This way dialog canceling (for example with Esc key) can be `event.preventDefault()`-ed if needed.

Native `` implementations (in Chrome for example) allow you to preventDefault the _cancel_ event, and so should the polyfill.

Example usage:

dialog.addEventListener("cancel", function (ev) {
ev.preventDefault();
});