The package must be in a git repository, so we first commit the changes.
git add .
git commit -m "some message"
Then every time we are going to publish a new version, we have to update the version number, so with that command, npm will automatically update the version for us.
npm version patch
In this case, we are writing the package in TypeScript but we want to publish it as JavaScript and add the TypeScript types separately, so with the build script, we are generating the corresponging files in the ./build folder (see package.json).
npm run build
Finally we can publish it to npm running the following command.
npm publish
If it's the first time publishing the package and it's public, we need to inidicate that through the following command.
npm publish --access public