Can I attach my own custom javascript to my form

Can I attach my own custom javascript to my form?

Is there a way to add a script to the html of my form?

Due to security reasons it's not possible to add JavaScript to a form, the HTML tags that you can use are a bit limited too. 

But if you require to add some JavaScript code for any reason, then you will need to get the source code of your form, this guide will help you getting that: https://www.jotform.com/help/104-How-to-get-the-Full-Source-Code-of-your-Form 

But note that each time that you make a change to your form you will need to re-embed your form with a fresh copy of the code. 

I hope this helps.