CLI: Execute command only on changed files

I use npm tasks as a build tool, I have these two tasks:

"scripts": {
    "build:js": "babel -d lib/ src/",
    "watch:js": "watch 'npm run build:js' src/"
}

Is there a way, using CLI, to execute babel only on a changed file? Something like:

"scripts": {
    "build:js": "babel -d lib/$CHANGED_FILE src/$CHANGED_FILE",
    "watch:js": "watch --only-changed 'npm run build:js' src/"
}

[Baudin999]

@elado as far as I know there is no convenient way. I’ve been struggling with this myself. But a lot of packages provide a watch themselves, babel is one of them:

"watch:js": "babel ./src/ --out-dir ./out/ --watch "

Another option is to not use the CLI and write out the watchTree code by hand in a file and run this as part of your build script.

Yet another option (this is the one I use) is to use the onchange package, it does not feel efficient, but it works…

onchange ./src/**/*.html -- bash ./scripts/training/temp.sh {{changed}}

The {{changed}} is the file path of the file changed. I pass this into another script, but that might be just a bit redundant.

PS, does not work with newly added files.

Hope it helps.

[TomasVotruba]

@elado Thanks for the answer. I try to use gulp, but it’s been kinda buggy - https://gist.github.com/TomasVotruba/dba01f73c2a502bbc4d693eeedc26a3a Almost there 😃