js_image_layer faq

why js_image_layer isn't like nodejs_image from rules_docker

That would require rules_js to take rules_docker as a dependency which would be not ideal given that rules_docker is in maintenance mode and other rulesets exists. So instead of being full-fledged js_image rule that is specific to one container building ruleset, it tries to be not opinionated and work with any ruleset out there.

why use custom builder script instead of using pkg_tar

There are two reasons why js_image_layer doesn't use pkg_tar.

1. It‘s a python dependency which we’d like to avoid
2. It doesn‘t work very well with ctx.actions.symlink. We needed to maintain a patch to make it work with rules_js which is specific to rules_js and can’t be pushed upstream.

Apart from that, pkg_tar is general and has more than needed here. maintaining 150LOC code is much easier than dealing with version skews and breaking changes in rules_pkg.

why check-in the image builder as minified javascript

There are number of reasons for this. Most significant one is not transpiling from ts to js anytime there is a cache miss on userland or at all for that matter. next one is convenience running .js files directly without fetching necessary toolchain to fetch dependencies and transpilers just to run a .ts file.