Run tsc -w, then another command after.
npm install tsc-thentsc -w will watch the filesystem and recompile your code almost instantly. Wouldn't you like to be able to run a command after it's done compiling? Like run your tests?
tsc-then is a super simple command that will run tsc -w and run a specified command after tsc -w is finished. It's ok if your command takes much longer than compiling, it will wait until the last run of your command is finished before starting the next one.
Because I'm generally editing with a smart editor that gives me inline errors, I left typescript's error reporting out of the console output, but this may change or become an option in a future version.
tsc-then -- npx mocha
This runs typescript's tsc -w, and each time compilation finishes, it runs the command npx mocha. It passes the stdout and stderr of npx mocha through, as well as some lines to delineate one run of the command from the next.
Pass in -p to specify a project directory or config file, the same as the -p argument to tsc. Pass it in multiple times, and tsc-then will run multiple tsc -w processes, one for each project, and it will first wait for all of them to compile, run your script, then it will run your script after any of them changes.