Bazel rules for js

EXPERIMENTAL this code is currently pre-release and not subject to any stability guarantee. It could be archived or there could be major breaking changes. Our goal is to eventually have rough feature parity with rules_nodejs “builtin”, but probably not until mid 2022 at the earliest.

This ruleset is a high-performance alternative to rules_nodejs.

The primary difference is that we don't run npm install or yarn install, instead we use a Bazel-idiomatic approach to managing the third-party dependencies.

Features include:

Only downloads packages from npm which are needed for the requested targets to be built/tested. #2121
Bazel downloader caches the npm package files, so no fetches are required when the repository rule is cache-busted.
Always represents npm packages as directories (TreeArtifact's in Bazel terminology) so there are few inputs to Bazel actions, making I/O operations much faster for setting up execroot/runfiles trees.
Uses the new “core” rules_nodejs which only downloads node.js for the requested platform and allows multiple versions.

See the design doc

In addition, as a clean rewrite many of the bugs in rules_nodejs are naturally resolved:

Drop four years of accumulated complexity.
No Bash dependency on Windows, #1102
nodejs_binary can be used as the tool in a genrule #1553, #2600
Repository layout matches the distribution so you can trivially patch or point to sources.
We use gazelle to generate bzl_library targets so users can always generate documentation for rules that reference these. #2874

Installation

From the release you wish to use: https://github.com/aspect-build/rules_js/releases copy the WORKSPACE snippet into your WORKSPACE file.

Usage

See the API documentation in the docs folder and the example usage in the example folder. Note that the example also relies on code in the /WORKSPACE file in the root of this repo.