- Lazy: only fetches/installs npm packages needed for the requested build/test targets.
- Correct: works seamlessly with node.js module resolution. For example there are no pathMapping issues with TypeScript
- Fast: Bazel's sandbox only sees npm packages as directories, not individual files.
- Supports npm "workspaces": nested npm packages in a monorepo.
https://blog.aspect.dev/rulesjs-npm-benchmarks shows benchmarks for fetching, installing, and linking packages under rules_js as well as typical alternatives like npm and yarn.
Google does not fund development of rules_js. If your company benefits, please consider donating to continue development and maintenance work: https://opencollective.com/aspect-build/projects/rules_js
- Remote Execution (RBE) requires the latest version of Bazel, 6.0.
- Building docker containers works, per this example however it requires some Starlark code which ought to be in our public API, see https://github.com/aspect-build/rules_js/issues/304
- No examples yet for stamping and publishing npm packages.
- ESM imports escape the runfiles tree and the sandbox due to https://github.com/aspect-build/rules_js/issues/362
rules_js is just a part of what Aspect provides:
- Need help? This ruleset has support provided by https://aspect.dev.
- See our other Bazel rules, especially those built for rules_js:
- rules_ts - Bazel rules for TypeScript
- rules_swc - Bazel rules for swc
- rules_jest - Bazel rules to run tests using Jest
- rules_esbuild - Bazel rules for esbuild JS bundler
- rules_webpack - Bazel rules for Webpack
- rules_jasmine - Bazel rules to run tests using Jasmine
- rules_cypress - Bazel rules to run tests using Cypress
From the release you wish to use:
copy the WORKSPACE snippet into your
See the documentation in the docs folder.
Basic usage examples can be found under the examples folder.
Note that the examples also rely on code in the
/WORKSPACEfile in the root of this repo.
Larger examples can be found in our bazel-examples repository including:
- Next.js / rules_ts
- Angular (cli/architect)
- Angular (ngc) / rules_ts
- React (create-react-app)
- Jest / rules_jest
- NestJS / rules_ts, rules_swc
Relationship to rules_nodejs
rules_js is an alternative to the
build_bazel_rules_nodejs Bazel module and
accompanying npm packages hosted in https://github.com/bazelbuild/rules_nodejs,
which is now unmaintained. All users are recommended to use rules_js instead.
rules_js replaces some parts of bazelbuild/rules_nodejs and re-uses other parts:
|Package manager and Basic rules|
|Toolchain and core providers|
The common layer here is the
rules_nodejs Bazel module, documented as the "core" in
rules_js does! It's a completely different approach to making JS tooling work under Bazel.
First, there's dependency management.
build_bazel_rules_nodejsuses existing package managers by calling
yarn installon a whole
rules_jsuses Bazel's downloader to fetch only the packages needed for the requested targets, then mimics
pnpmto lay out a
Then, there's how a nodejs tool can be executed:
build_bazel_rules_nodejsfollows the Bazel idiom: sources in one folder, outputs in another.
rules_jsfollows the npm idiom: sources and outputs together in a common folder.
There are trade-offs involved here, but we think the
rules_js approach is superior for all users,
especially those at large scale. Read below for more in-depth discussion of the design differences
and trade-offs you should be aware of.
Also see the slides for our Bazel eXchange talk
There are two core problems:
- How do you install third-party dependencies?
- How does a running nodejs program resolve those dependencies?
And there's a fundamental trade-off: make it fast and deterministic, or support 100% of existing use cases.
Over the years we tried a number of solutions and each end of the trade-off spectrum.
Installing third-party libraries
Downloading packages should be Bazel's job. It has a full featured remote downloader, with a content-address-cached (confusingly called the "repository cache"). We now mirror pnpm's lock file into starlark code, then use only Bazel repository rules to perform fetches and translate the dependency graph into Bazel's representation.
For historical context, we started thinking about this in February 2021 in a (now outdated) design doc and have been working through the details since then.
Running nodejs programs
Fundamentally, Bazel operates out of a different filesystem layout than Node. Bazel keeps outputs in a distinct tree outside of the sources.
Our first attempt was based on what Yarn PnP and Google-internal nodejs rules do:
monkey-patch the implementation of
require in NodeJS itself,
so that every resolution can be aware of the source/output tree difference.
The main downside to this is compatibility: many packages on npm make their own assumptions about
how to resolve dependencies without asking the
require implementation, and you can't patch them all.
Unlike Google, most of us don't want to re-write all the npm packages we use to be compatible.
Our second attempt was essentially to run
npm link before running a program, using a runtime linker.
This was largely successful at papering over the filesystem layout differences without disrupting
execution of programs. However, it required a lot of workarounds anytime a JS tool wanted to be
aware of the input and output locations on disk. For example, many tools like react-scripts (the
build system used by Create React App aka. CRA) insist on writing their outputs relative to the
working directory. Such programs were forced to be run with Bazel's output folder as the working
directory, and their sources copied to that location.
rules_js takes a better approach, where we follow that react-scripts-prompted workaround to the
extreme. We always run JS tools with the working directory in Bazel's output tree.
We can use a
pnpm-style layout tool to create a
bazel-out, and all resolutions
This third approach has trade-offs.
- The benefit is that very intractable problems like TypeScript's
rootDirsjust go away. In that example, we filed https://github.com/microsoft/TypeScript/issues/37378 but it probably won't be solved, so many users trip over issues like this and this. Now this just works, plus results like sourcemaps look like users expect: just like they would if the tool had written outputs in the source tree.
- The downside is that Bazel rules/macro authors (even
genruleauthors) must re-path inputs and outputs to account for the working directory under
bazel-out, and must ensure that sources are copied there first. This forces users to pass a
BAZEL_BINDIRin the environment of every node action. https://github.com/bazelbuild/bazel/issues/15470 suggests a way to improve that, avoiding that imposition on users.