Required inputs

Hello,
I am currently using a multi-step form, and on a page there is a checkbox that if selected some input fields become required, but if I leave these required fields in the default form in the field and these are not filled in, the submission will not proceed.
My question is whether there is an option to use the $form object in JavaScript, to enable this field to be required by default using JavaScript in the moment the checkbox field is selected, I am currently using JavaScript to make these input fields required in the HTML, but this is not an elegant way.
Thank you.