Indeed it can't. But you can get close. The key is that the side-effect has to be much more granular. Instead of re-rendering a virtual dom for an entire component as a side-effect, the side-effect is changing a single attribute on an element, or updating its list of children.

This means using a template language where one can make these associations between variables and DOM. JSX doesn't work here because its output could be anything.

I am toying with an experimental framework that implements these ideas. I am convinced we can do better than diffing vdoms.