Subscription form with validation and success page

Hi! I have a couple of questions:

• I made two pages, one for the form, the other is a success page. The validation of the form is triggered when the user clicks on the form button. The problem is that the event listener for the button throws an error when i am on the success.html page because it can't find any button ("Cannot read property 'addEventListener' of null" or something). To solve this I put the event listener in an if statement, so that it triggers the event listener only if the element exists. Is this best practice? Are there better ways to do this?

• Regarding accessibility and aria roles, do you know any resource that explains the basics of using the aria roles in forms?

Thank You.