How to get parent page field value from detail?

Hi community,

I've added a custom button in the product in order detail in the order page. But I need to hide this detail custom button when a field, say fieldA, in the order page has the value of 0; and display the detail custom button immediately when user change the value of fieldA to a value greater than 0.

Take it brief, I need to use fieldA as a toggle. When fieldA>0, the detail custom button displays; when fieldA<=0, the detail custom button hides.

Thank you in advance!