Migrating from rules_nodejs? Start at the Migration Guide
- See the Frequently asked questions
- Ask in
- Check for known issues
- Pay for support, provided by https://aspect.dev.
From the release you wish to use:
copy the WORKSPACE snippet into your
BUILD.bazel files are used to declare the dependency graph of your code.
They describe the source files and their dependencies, and declare entry points for programs or tests.
However, they don't say how to build the code, that's the job of Bazel rules.
BUILD files typically declare a finer-grained dependency graph than
package.json files, Bazel can be smarter about what to fetch or invalidate for a given build.
For example, Bazel might only need to fetch a single npm package for a simple build,
where you might experience other tools installing the entire
On the other hand, authoring BUILD files is a chore that's required under Bazel and not in other tools like Rush or Nx. We plan a Gazelle extension soon which automates much of this toil.
rules_js depends on rules_nodejs version 5.0 or greater.
Installation is included in the
WORKSPACE snippet you pasted from the Installation instructions above.
- Choosing the version of Node.js: https://bazelbuild.github.io/rules_nodejs/install.html
- Rules API: https://bazelbuild.github.io/rules_nodejs/Core.html
- The Node.js toolchain: https://bazelbuild.github.io/rules_nodejs/Toolchains.html
Fetch third-party packages from npm
rules_js accesses npm packages using pnpm.
pnpm's "virtual store" of packages aligns with Bazel's "external repositories",
and the pnpm "linker" which creates the
node_modules tree has semantics we can reproduce with Bazel actions.
If your code works with pnpm, then you should expect it works under Bazel as well. This means that if your issue can be reproduced outside of Bazel, using a reproduction with only pnpm, then we ask that you fix the issue there, and will close such issues filed on rules_js.
The typical usage is to import an entire
Create such a file if you don't have one. You could install pnpm on your machine, or use
npx to run it.
For example, this command creates a lockfile with minimal installation needed:
npx pnpm install --lockfile-only
Next, you'll typically use
npm_translate_lock to translate the lock file to Starlark, which Bazel extensions understand.
WORKSPACE snippet you pasted above already contains this code.
npm_translate_lock, you have two choices:
loadfrom the generated
WORKSPACE, like the
WORKSPACEsnippet does. This will cause every Bazel execution to evaluate the
npm_translate_lock, making it "eager". The execution is fast and only invalidated when the
pnpm-lock.yamlfile changes, so we recommend this approach.
- Check the generated
repositories.bzlfile into your version control, and
loadit from there. This fixes the "eager" execution, however it means you need some way to ensure the file stays up-to-date as the
pnpm-lock.yamlfile changes. This approach can be useful for bazel rules which want to hide their transitive dependencies from users. See https://github.com/bazelbuild/rules_python/issues/608 for a similar discussion about rules_python
pip_parsewhich is similar.
Technically, we run a port of pnpm rather than pnpm itself. Here are some design details:
- You don't need to install pnpm on your machine to build and test with Bazel.
- We re-use pnpm's resolver, by consuming the
pnpm-lock.yamlfile it produces.
- We use Bazel's downloader API to fetch package tarballs and extract them to external repositories. To modify the URLs Bazel uses to download packages (for example, to fetch from Artifactory), read https://blog.aspect.dev/configuring-bazels-downloader.
- We re-use the
@pnpm/lifecyclepackage to perform postinstall steps. (These run as cacheable Bazel actions.)
- Finally, you link the
node_modulestree by adding a
BUILDfile, which populates a tree under
After importing the lockfile, you should be able to fetch the resulting repository.
npm_translate_lock was named
npm, you can run:
bazel fetch @npm//...
Link the node_modules
Next, we'll need to "link" these npm packages into a
If you use pnpm workspaces, the
node_modules tree contains first-party packages from your
monorepo as well as third-party packages from npm.
Bazel doesn't use the
node_modulesinstalled in your source tree. You do not need to run
pnpm installbefore running Bazel commands. Changes you make to files under
node_modulesin your source tree are not reflected in Bazel results.
Typically, you'll just link all npm packages into the Bazel package containing the
If you use pnpm workspaces, you will do this for each npm package in your monorepo.
load("@npm//:defs.bzl", "npm_link_all_packages") npm_link_all_packages()
You can see this working by running
bazel build ..., then look in the
You'll see something like this:
# the virtual store bazel-bin/node_modules/.aspect_rules_js # symlink into the virtual store bazel-bin/node_modules/some_pkg # If you used pnpm workspaces: bazel-bin/packages/some_pkg/node_modules/some_dep
- npm_import: Import all packages from the pnpm-lock.yaml file, or import individual packages.
- npm_link_package: Link npm package(s) into the
bazel-bin/[path/to/package]/node_modulestree so that the Node.js runtime can resolve them.
The Node.js module resolution algorithm requires that all files (sources, generated code, and dependencies) be co-located in a common filesystem tree, which is the working directory for the Node.js interpreter.
As described earlier, the dependencies were linked into
and Bazel places generated files in
bazel-bin/[path/to/package]. This leaves source files to be
copied to this location.
Copying sources to the bazel-bin folder is surprising if you come from a Bazel background, as other Bazel rulesets accomodate tooling by teaching it to mix a source folder and an output folder. This is not possible with Node.js, without breaking compatibility of many tools.
Our custom rules will take care of copying their sources to the
bazel-bin output folder automatically.
However this only works when those sources are under the same
BUILD file as the target that does
the copying. If you have a source file in another
BUILD file, you'll need to explicitly copy that
with a rule like
- js_library: Declare a logical grouping of JS files and their dependencies.
- js_binary: Declare a Node.js executable program.
- js_run_binary: Run a Node.js executable program as the "tool" in a Bazel action that produces outputs, similar to
Using binaries published to npm
rules_js automatically mirrors the
bin field from the
package.json file of your npm dependencies
to a Starlark API you can load from in your BUILD file or macro.
For example, if you depend on the
typescript npm package, you write this in
load("@npm//:typescript/package_json.bzl", typescript_bin = "bin") typescript_bin.tsc( name = "compile", srcs = [ "fs.ts", "tsconfig.json", "//:node_modules/@types/node", ], outs = ["fs.js"], chdir = package_name(), args = ["-p", "tsconfig.json"], )
Note: this doesn't cause an eager fetch! Bazel doesn't download the typescript package when loading this file, so you can safely write this even in a BUILD.bazel file that includes unrelated rules.
To inspect what's in the
@npm workspace, start with a
bazel query like the following:
bazel query @npm//... --output=location /shared/cache/bazel/user_base/581b2ac03dd093577e8a6ba6b6509be5/external/npm/BUILD.bazel:24:12: bzl_library rule @npm//:@types/node /shared/cache/bazel/user_base/581b2ac03dd093577e8a6ba6b6509be5/external/npm/BUILD.bazel:17:12: bzl_library rule @npm//:typescript /shared/cache/bazel/user_base/581b2ac03dd093577e8a6ba6b6509be5/external/npm/examples/macro/BUILD.bazel:19:12: bzl_library rule @npm//examples/macro:mocha /shared/cache/bazel/user_base/581b2ac03dd093577e8a6ba6b6509be5/external/npm/examples/macro/BUILD.bazel:5:12: bzl_library rule @npm//examples/macro:mocha-junit-reporter /shared/cache/bazel/user_base/581b2ac03dd093577e8a6ba6b6509be5/external/npm/examples/macro/BUILD.bazel:12:12: bzl_library rule @npm//examples/macro:mocha-multi-reporters
This shows locations on disk where the npm packages can be loaded.
To see the definition of one of these targets, you can run another
bazel query --output=build @npm//:typescript /shared/cache/bazel/user_base/581b2ac03dd093577e8a6ba6b6509be5/external/npm/BUILD.bazel:17:12 bzl_library( name = "typescript", visibility = ["//visibility:public"], srcs = ["@npm//:typescript/package_json.bzl"], deps = ["@npm__typescript__4.7.2//:typescript"], )
This shows us that the label
@npm//:typescript/package_json.bzl can be used to load the "bin" symbol. You can also follow the location on disk to find that file.
Each bin exposes three rules, one for each Bazel command ("verb"):
Bazel macros are a critical part of making your BUILD files more maintainable. Make sure to follow the Style Guide when writing a macro, since some anti-patterns can make your BUILD files difficult to change in the future.
Like Custom Rules, Macros require you to use the Starlark language, but writing a macro is much easier since it merely composes existing rules together, rather than writing any from scratch. We believe that most use cases can be accomplished with macros, and discourage you learning how to write custom rules unless you're really interested in investing time becoming a Bazel expert.
You can think of Macros as a way to create your own Build System, by piping the existing tools together (like a unix pipeline that composes command-line utilities by piping their stdout/stdin).
As an example, we could write a wrapper for the
typescript_bin.tsc rule above.
tsc.bzl we could write:
load("@npm//:typescript/package_json.bzl", typescript_bin = "bin") def tsc(name, args = ["-p", "tsconfig.json"], **kwargs): typescript_bin.tsc( name = name, args = args, # Always run tsc with the working directory in the project folder chdir = native.package_name(), **kwargs )
so that the users
BUILD file can omit some of the syntax and default settings:
load(":tsc.bzl", "tsc") tsc( name = "two", srcs = [ "tsconfig.json", "two.ts", "//:node_modules/@types/node", "//examples/js_library/one", ], outs = [ "two.js", ], )
If macros are not sufficient to express your Bazel logic, you can use a custom rule instead. Aspect has written a number of these based on rules_js, such as:
- rules_ts - Bazel rules for the
tsccompiler from http://typescriptlang.org
- rules_swc - Bazel rules for the swc toolchain https://swc.rs/
- rules_jest - Bazel rules to run tests using https://jestjs.io
- rules_esbuild - Bazel rules for https://esbuild.github.io/ JS bundler
- rules_webpack - Bazel rules for webpack bundler https://webpack.js.org/
- rules_deno - Bazel rules for Deno http://deno.land
You can also write your own custom rule, though this is an advanced topic and not covered in this documentation.
Documenting your macros and custom rules
You can use stardoc to produce API documentation from Starlark code.
We recommend producing Markdown output, and checking those
.md files into your source repository.
This makes it easy to browse them at the same revision as the sources.
You'll need to create
bzl_library targets for your Starlark files.
This is a good practice as it lets users of your code generate their own documentation as well.
In addition, Aspect's bazel-lib provides some helpers that make it easy to run stardoc and check that it's always up-to-date.
Continuing our example, where we wrote a macro in
tsc.bzl, we'd write this to document it, in
load("@aspect_bazel_lib//lib:docs.bzl", "stardoc_with_diff_test", "update_docs") load("@bazel_skylib//:bzl_library.bzl", "bzl_library") bzl_library( name = "tsc", srcs = ["tsc.bzl"], deps = [ # this is a bzl_library target, exposing the package_json.bzl file we depend on "@npm//:typescript", ], ) stardoc_with_diff_test( name = "tsc-docs", bzl_library_target = ":tsc", ) update_docs(name = "docs")
This setup appears in examples/macro.
Create first-party npm packages
You can declare an npm package from sources in your repository.
The package can be exported for usage outside the repository, to a registry like npm or Artifactory. Or, you can use it locally within a monorepo using pnpm workspaces.
Note: we don't yet document how to publish. For now, build the
bazel build, then
bazel-outfolder where the package was created, and run