Jupyterlab dev watch mode doesn't work

Hi Guys,
I’m trying to build a basic extension for Jupyterlab in Javascript.
Having a hard time to cut down on rebuilding time while in watch mode.

jupyter lab --dev-mode --watch

It does not work as expected. After each source file changes, it takes about a minute to pick
up the change but sometimes it does not respond to changes at all.
I also run watch command in parallel, but it does not help either
package.json script:
"watch": "tsc -w --listEmittedFiles"

Any idea on how it could be improved?