Sure but the command line version as best I can tell doesn’t bother keeping a long-lived tsc around. Sure, you can run it in watch mode but if you just run it it doesn’t bother doing that. For example, Facebook launches watchman to keep track of file modifications to files and keeps Buck’s dependency graph up to date so that Buck knows which targets are out of date instantly when you run the command. A more advanced version would know which targets you rebuild/run when you make a change like that and automatically refresh them. Same for running the tests.