NPM has some powerful built-in scripts that can be used inside a package.json file. Scripts have built-in pre and post lifecycle hooks that help you control these processes to some degree. If the process(es) are more complicated, this may be too simplistic for your needs, but it's nice to know that they're available.
You can do something like this:
"scripts": {
"prestart": "echo 'preparing build...'",
"poststart": "echo 'process finished.'",
"start": "rollup -c"
}This is pretty contrived, but you'll get preparing build... before Rollup compiles your build, and then process finished. after compilation finishes when you run the start script.
A common scenario might be to build your code prior to publishing:
"scripts": {
"prepublishOnly": "rollup -c",
}(prepublish was deprecated in favor of prepare, and it runs before a variety of different scenarios. Use prepublishOnly to run a script prior to publishing only).
Something that's really neat is that you can use any custom string for a script, and the pre and post versions of that script will work. For instance:
"scripts": {
"prefoo": "echo 'preparing build...'",
"postfoo": "echo 'process finished.'",
"foo": "rollup -c"
}