I'm not advocating it (nor am I against it for that matter) but generic shopping cart modules have for a long time supported adding to the cart via URLs. It's quite a practical design as you just store a shopping cart URL with your product catalog data/page, and was kind of the starting point for "web services" and the composable web (until SOAP and REST ruined it with dogma wrt what you should and shouldn't do).
We had online stores even before JavaScript existed. All you need are cookies and form submission. Actually, as mentioned in another post, you don't even really need cookies.
We had stores even before online stores existed. All you needed is to go there.
By using form submission like in the good old Web 1.0 days.