Is there a shared application that comes with some examples of using javascript

I don't think there is any specific sample application that as examples of JS validations. But there are several applications on this topic, and many threads that talk about JS/validations (especially the older posts). You can search for some of these posts. For example, here is one such link forum.appian.com/.../b-24981, and another one - forum.appian.com/.../b-22913. Do keep in mind that when using JS on your forms, your forms are no longer mobile supported and is not a best practice.

Thanks. Even though there is no use case for mobile now, I would like to keep the application inline with best practices so that we don't have to do a lot of rework when we do have an use case for mobile.
So if we have to keep it mobile enabled, Javascript of any sort is a strict NO-NO?

Yes, JavaScript isn't supported on mobile enabled forms.