What problem does this feature solve?

Please provide detailed documentation of "@vue/reactivity" in order to use it outside of the vue application.

I found that "@vue/reactivity" might be a better mobx. Developers can use "@vue/reactivity" in react as a global state manager!

What does the proposed API look like?

Please provide detailed documentation of "@vue/reactivity" in order to use it outside of the vue application.

All the documentation is already in Vue docs

The API is documented here, which is 99% of what one might need: https://v3.vuejs.org/api/reactivity-api.html

You can open an issue in the docs repo asking for a little usage intro on standalone usage. That might fit well on the Page I linked above.

"@vue/reactivity" It does not export the "watch" method, it has the "effect" method, which is not written in the documentation.

@masx200 there is no watch method in reactivity. use effect instead. BTW, watchEffect is a part of runtime-core. 请仔细阅读文档.