chronoforms v5 - submit button disable

Question

I'm trying to make my button disable but when I use the method described here... But my contact page won't load at all, giving me a 500 error.

Firstly, I've placed a Load Javascript above the HTML Render - and here I've placed my function.

function disableSubmit(){
  $('submitButton').disabled = true;
  $('submitButton').value = 'Processing . . .';
};

Then I did the following as described...

Add a Custom code action to your form OnLoad event and put this code into it*:

<?php
$form->form_params->set('jsvalidation_onValidateSuccess', 'showLoader');
?>

Is there a different method in Chronoforms v5 that I should be using?

Appreciate the assistance everyone.

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chronoforms v5 - submit button disable