[Vuejs]-Vue3 Plugin giving error 'does not provide an export named 'default'' – how do I export it?

At the top of alert.js I have changed

const Alert = {}

to

export const Alert = {}

I had tried this before posting my question, but it didn’t make any difference to start with. I have now found that it is necessary to stop the Vite server, and re-start it, to update a plugin – it doesn’t hot reload! Of course.