I've seen references to getCurrentInstance() function on some old(?) documents and codes, but cannot find it in the current Vue 3 document.
Is getCurrentInstance() deprecated?
If so, what is the reason? (inject() considered enough?) If not, why can't I find it in the document?
getCurrentInstance() was removed from the Vue 3 docs because it's an internal API:
Because the instance is an internal instance that exposes non-public APIs. Anything you use from that instance can technically break between any release types, since they are not subject to semver constraints.
getCurrentInstance() was originally documented in 4-Oct-2020, but that was later removed in 31-Aug-2021 in a major refactoring of the Composition API docs by the creator of Vue (Evan You). Despite its removal from the docs, getCurrentInstance() still:
Given that it's an undocumented internal API, use it with caution.
https://github.com/vuejs/vue/issues/12596#issuecomment-1173269807
quoting the comment from evan,
getCurrentInstance is used mostly for official vue libraries that need additional internal access, not for userland application code. It was mistakenly documented in WIP v3 docs but is no longer considered a public API
