Advanced Checkout Hosted Fields, Validate Form, "Subscribe to multiparty card field events", where??

[GrizzT]

Hope this is the right place. 

I am integrating the hosted fields and have it working, but I want to validate the credit card fields to check if they are empty before submitting the form.

I am doing pretty much the same as here. Which I found from [Removed]

Subscribe to multparty card field events seems to be what I need, but I can not figure out how to get it to work. 

How to check the fields before submitting with the code in the first link?

Thank you