Can I run some code whenever a file is changed?

When I change an html file on my server can I run a couple lines of javascript?

We don’t currently support webhooks for edit events, but you could use a watch.json file (https://glitch.com/edit/#!/project/watch-json) to cause editing HTML files to trigger a restart, and then add calling a particular js file to your start command or include those few lines in whatever server js file you’re currently running.