Not letting customer order more than 1 product

[OriyanJ]

VirtueMart 3.0.11.4

I want the customer to only be able to order a certain product at a time. They can have quantity, but not 2 or more different products.
Let's say that I want to let them order headphones, but only that, for example. They can order 12 of them, but they can't order a laptop at the same order.

[GJC Web Design]

JS or PHP in the cart?

if 2 or more products found disable the checkout button and show a message

[OriyanJ]

I thought about maybe that when customer tried to order another product, the cart's session ends first and then being created again. Or maybe when leaving cart's page, clear it.

[GJC Web Design]

seems complicated .. just don't let them checkout if they have more than 1 object in their $cart->products and tell them what is happening