I need to get to the Customer on a transaction from the line level Inventory Detail pop-up window. I'm trying to use window.opener to get a handle to the transaction that pops up the inventory detail screen (for example an Item Fulfillment or Sales Order). The "opener" portion is null which seems to point to how the window is actually opens. Its null due to how the window was opened by netsuite. I want to get to the Customer on the transaction but due to not getting a handle to the opening window, you can't as that info isn't on the Inventory Detail record. Is there a better way to do this that I am not seeing?

not sure what you're trying to complete and so, whilst I think you need to look beyond the Inventory Detail record, I cant recommend where to look, from your story I think it's best to move away client side, and that's all I can recommend With the subrecord I can totally see it works server side, say even suitelet an then say executing at a higher role it'll probably do what you want it to

its done via an iframe

Its def an iframe lemme try the parent instead. I'm gonna feel stupid if that works.