update-notifier serves the purpose here. As from the tagline, Inform users of your package of updates in a non-intrusive way.
Hi @yangshun I've been working on this in my fork and have had some success getting the notification to display in testing for v 1.x. when I hard code the old version per update-notifier's testing instructions. I'd be glad to be assigned the issue to implement this feature.

@strtw are you still working on this?
This would be a really cool feature to add!
@jamesgeorge007 Haven't since my last post but would be glad to be assigned and continue working on it
@strtw go for it! Although before it would be nice to bring to completion of your previous PR https://github.com/facebook/docusaurus/pull/2282
We'd love to have this feature! @strtw is this something you're still working on?
@strtw if you're caught up, I can work on a PR.
@jamesgeorge007 Yah of course! Here's a link to the draft PR I submitted in case it helps. https://github.com/facebook/docusaurus/pull/2890
I'll work on this for v2 :)
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Hi @yangshun I've been working on this in my fork and have had some success getting the notification to display in testing for v 1.x. when I hard code the old version per update-notifier's testing instructions. I'd be glad to be assigned the issue to implement this feature.