This runs babel on files that have been modified since the last run only, unless the last run failed (non-zero exit code) in which case the cache will not be reconciled and previously modified files will be re-transpiled (otherwise the cache reconcile will cause un-transpiled files to be missed if there is an error on a different file). It uses file-entry-cache. The first run will have no modification times saved yet so it will run on all files. Note: To delete the file stat cache so that the next run will include all files, use the command babel-changed --reset.

This is just an alternative to using --watch for weird people like me that never got in the habit of doing that.

Install

npm i -D babel-changed

Note: you will need to also install babel as per usual.

Usage

Note: I have tested this on my own computer with just my own simple babel command. Beyond that it may not work right, so YMMV.

Put something close to this in your scripts (note that the first argument is the source directory):

"build": "babel-changed src -d lib",
"clean": "babel-changed --reset"

Then, assuming babel, babelrc, plugins etc. are all set up, run:

npm run build

If there are modified files detected it will mention the number and pass a list of them as an --only option to babel. Otherwise it won't do anything. To rebuild everything next time, run npm run clean (no other arguments).

FYI, It spawns babel with pty.js. Also the file stat data is in node_modules/flat-cache/.cache/.