JavaScript Reactivity Engines Use Javascript Proxies

With view three with this proxy reactivity approach the proxy is the one tracking all the deepness and the underlying object doesn't change which feels really nice. You can mutate that underlying object as you please so you can add properties and they will be able to access them no matter what even if x doesn't exist. So it's more flexible and that's why a lot of reactivity engines use javascript proxies like i don't really know of any new ones that are using the getter and setter approach anymore because proxies are so powerful.