Today Sebastian wondered:

Disabling a form submit button while submitting: yay or nay?

(I thought I saw some research that discourages it, but can't remember where or why)

— Sebastian De Deyne (@sebdedeyne) November 4, 2020

I quickly chimed in saying that I do tend to lock up forms when submitting them. Let me explain why …

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I started locking up submitted forms as users of the apps I’m building reported that sometimes the actions they had taken — such as adding an entry — were performed twice. I took me some time to figure out what exactly was going on, but eventually I found out this was because they were double clicking the submit button of the forms. As they double clicked the button, the form got sent over twice. By locking up forms after their first submission, all successive submissions — such as those triggered by that second click of a double click — are ignored.

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To prevent these extra form submissions from being made I don’t hijack the form with Ajax nor do I perform any other complicated things. I let the inner workings of the web and forms in the browser be: when pressing the submit button the browser will still collect all form data, build a new HTTP request, and execute that request.

What I simply do is extend the form’s capabilities by adding a flag — by means of a CSS class — onto the form to indicate whether it’s being submitted or not. I can then use this flag’s presence to deny any successive submissions, and also hook some CSS styles on. — Progressive Enhancement, Yay! 🎉

The code looks as follows:

 // Prevent Double Submits
document.querySelectorAll('form').forEach(form => {
	form.addEventListener('submit', (e) => {
		// Prevent if already submitting
		if (form.classList.contains('is-submitting')) {
			e.preventDefault();
		}
		
		// Add class to hook our visual indicator on
		form.classList.add('is-submitting');
	});
});

With that .is-submitting class in place, we can then attach some extra CSS onto the form to give the user visual feedback. Here’s a few examples:

See the Pen
Prevent Form Double Submits by Bramus (@bramus)
on CodePen.

See the Pen
Prevent Form Double Submits (Alternative version) by Bramus (@bramus)
on CodePen.

Note that this solution might not cover 100% of all possible scenarios, as it doesn’t take failing networks and other things that might go wrong into account. However, as I’m relying on the basic mechanisms of the web I think I can also rely on the browser to show that typical “Confirm Form Resubmission” interstitial should a timeout occur. Additionally, if need be, one could always unlock the form after a fixed amount of time. That way the user will be able to re-submit it again.

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Dealing with double form submissions isn’t a new issue at all. You’ll find quite some results when running a few queries through Google — something I only found out after stumbling over the issue myself.

Back in 2015 (!) Mattias Geniar also pondered about this, after being pulled into the subject from a sysadmin view. Now, when even sysadmins are talking about an HTML/UX issue you know there’s something going on. This made me wonder why browsers behaved like that and how we could solve it:

🤔 Why is it that browsers don't prevent double form submissions by default? Some users (mistakingly) double click on submit buttons.

💡 An attribute on <form> to tweak this behavior – instead of having to rely on JavaScript – would come in handy …

/cc @WHATWG @w3c

— Bramus! (@bramus) February 13, 2020

As a result I decided to open an issue at the WHATWG HTML Standard repo, suggesting for a way to fix this at spec level:

An attribute on <form> to tweak this behavior – instead of having to rely on JavaScript – would come in handy and form a nice addition to the spec.

I see two options to go forward:

1. Browsers/the standard keeps the current behavior and allow multiple submits. Developers must opt-in to prevent multiple submissions using a preventmultiplesubmits attribute.
2. Browsers/the standard adjust the current behavior to only submit forms once. Developers must opt-in to allow multiple submissions using a allowmultiplesubmits attribute.

Initial response on the issue was very low, and it looks like this isn’t that big of a priority.

Back then I was more in favor of the second solution, but now I’m quite undecided as changing the default behavior — which has been around for ages — is quite tricky.

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Another way that this issue could be fixed is at the browser level: if they were to treat double clicks on form submit buttons as single clicks, then the double click problem — but not the double submit problem — could also be taken care of.

To then attach styles to forms being submitted a CSS Pseudo Class :submitting would come in handy. Come to think of it, this Pseudo Class would be a quite nice addition to CSS in itself, no matter whether this double click issue gets solved or not.

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Winging back to the addition to the HTML spec I suggested: If you do think it could be something the HTML spec could benefit from, feel free to add a thumbs up to the issue to indicate that you want this, or add an extra comment to it if you have more input on the subject.