[leepowers]

An important caveat to the "load scripts at the end of the document technique": The visual elements of a page will render before the functional components (i.e., JavaScript) are available.

Imagine a site the sets a custom `submit` handler for a `<form>` tag, possibly for client-side form validation, an AJAX file uploader, date selection, etc. A user submits the form before JavaScript has loaded completely and doesn't get the benefit of the JavaScript-enhanced experience. In local development or on a high-speed connection this will probably never happen. But a user accessing the site with their phone over the slow U.S. cell data network has a much higher chance of hitting upon this undesired behavior.

[Cyranix]

Would it be acceptable to set the form's submit button to disabled in the HTML, attaching the custom event handler and enabling the submit button in a document-final script? Seems like you still get reasonable behavior in the low-bandwidth environment -- maybe even better, since the user can now access the other elements of the form while the script is being loaded and run.

[bluesmoon]

That's an accessibility issue for users with JavaScript disabled (or where JavaScript fails to load).

On the other hand, it's also the recommended method to protect your users from a click-jacking attack across all browsers (read those that don't support CORS).