What’s usually expected when transitioning stacks?

I’ve been a Ruby on Rails developer for about 3 years, and for the past 6 months I’ve been working professionally with JavaScript and React.

I recently saw a job listing for a mid level React developer asking for 2+ years of React experience. This made me wonder, in cases like this, do companies usually expect 2 full years of React-specific experience, or are they looking for someone with mid level experience overall, who happens to be working in React?

In my case, I’m confident with React, but obviously I don’t have 2 years with the framework.

In cases like this where a developer changes stacks, does the “experience counter” go back to 0 years? I really don’t know what is expected.