JetFormBuilder. JS. Do something while form is submitting

code.html

<script>
	document.addEventListener( 'DOMContentLoaded', function() {

		if ( ! window.JetPlugins ) {
			return;
		}

		const $forms = document.querySelectorAll( '.jet-form-builder' );

		if ( ! $forms.length ) {
			return;
		}

		// Tracks start of the form processing
		$forms.forEach( function( $form ) {
			$form.addEventListener( 'submit', function( event ) {
				// Here we're doing what we need on submit start
				event.target.style.backgroundColor = 'red';
			} );
		} );

		// Callback performed on the end of the form processing
		function onFormSubmit() {
			// Here we're doing what we need on submit end
			this.formNode.style.backgroundColor = 'transparent';
		}

		// Tracks end of the form processing
		window.JetPlugins.hooks.addAction( 'jet.fb.observe.after', 'checkStart', function( observable ) {
			observable.form.submitter.status.formNode = observable.rootNode;
			observable.form.submitter.status.watch( onFormSubmit );
		} );
	} );
</script>