Nextjs export clear "out" folder - next.js

Question

I'm working with nextjs and this example https://github.com/zeit/next.js/tree/master/examples/with-static-export
in next.config.js i have code:
module.exports = {
async exportPathMap(defaultPathMap, { dev, dir, outDir, distDir, buildId, incremental }) {
// we fetch our list of posts, this allow us to dynamically generate the exported pages
const response = await fetch(
'https://jsonplaceholder.typicode.com/posts?_limit=3'
)
const postList = await response.json()
// tranform the list of posts into a map of pages with the pathname `/post/:id`
const pages = postList.reduce(
(pages, post) =>
Object.assign({}, pages, {
[`/post/${post.id}`]: { page: '/post/[id]' },
}),
{}
)
// combine the map of post pages with the home
return Object.assign({}, pages, {
'/': { page: '/' },
})
},
}
Its fetch 3 posts and generate files - [id].html - its great!
But now i need to fetch new post and build page only for this new post but commad next export remove all files from out and create only one post.
What i need to do to keep old post and add new one on next export?
Example:
First next export with request for 3 posts from api
generate 3 post in folder "out"
change api url and run next export for 1 new post
summary i have 3 old post pages and 1 new in my "out" directory
How to do that?

Answer 1

Next can't do this out of the box, but you can set it up to do so. First, you'll need a system (database) of which pages have already been built. Second, you'll need some method of communicating with that database (api) to ask which pages should be built (eg, send over a list of pages and the api responds telling you which ones have not yet bene built). Then, tell your exportPathMap which pages to build. And finally, move your built pages out of out and into a new final/public directory.
By default, Next will build/export anything in the pages directory plus anything you set in exportPathMap, and put all of those in the out directory. You can override what it builds by passing a custom exportPathMap, and how you handle what goes into the out directory is up to you, so you can move those files to a different actual public directory and merge them with the old files.