Hello fellow group members!

I am a point and click Admin running into a situation were a custom JavaScript Button we use on an a custom Agreement object enforces that an Opportunity is in a certain stage before the button will run, or else the user gets an error message. So basically a validation rule, but in the JavaScript code. 

Since JavaScript buttons don't work in LEX, the LEX button convertor isn't capturing these buttons, and I am not a developer, I was wondering if anyone knew of a non-code solution to enforce validation rules upon utilizing a quick action. I'm also open to some REALLY light coding (similar to what was done with the JavaScript buttons) if that's the only solution.

Thanks in advance for the help!