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HTML

              
                <form>
	<input />
	<input type="submit" />
</form>

<footer>
	<p>Demo for <a href="https://www.bram.us/2020/11/04/preventing-double-form-submissions/">https://www.bram.us/2020/11/04/preventing-double-form-submissions/</a></p>	</footer
              
            
!

CSS

              
                form {
	position: relative;
	display: inline-block;
}

/** Don't like the overlay being used here? Check https://codepen.io/bramus/pen/NWrzmrV for an alternative version which animates the submit button **/

form.is-submitting::before {
	position: absolute;
	content: '';
	top: -0.5em;
	right: -0.5em;
	left: -0.5em;
	bottom: -0.5em;
	background: rgba(0,0,0,0.2) url('data:image/svg+xml;base64,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') no-repeat 50% 50% / 1em 1em;
}



/** ONLY NON-DEMO RELATED STYLES BELOW **/
body {
	height: 100vh;
	display: flex;
	flex-direction: column;
	align-items: center;
	justify-content: center;
}

footer {
	margin-top: 5em;
	font-style: italic;
	font-size: 0.8em;
}
              
            
!

JS

              
                // Prevent Double Submits
document.querySelectorAll('form').forEach(form => {
	form.addEventListener('submit', (e) => {
		// Prevent if already submitting
		if (form.classList.contains('is-submitting')) {
			e.preventDefault();
			console.info('Successive submit suppressed');
		}
				
		// Add a visual indicator to show the user it is submitting
		form.classList.add('is-submitting');
	});
});


// Extra snippet here to also prevent form submissions the first submit
// as a viewer of this demo would otherwise be guided to outside of CodePen …
document.querySelectorAll('form').forEach(form => {
	form.addEventListener('submit', e => {
		e.preventDefault();
	});
});
              
            
!
999px

Console