Generated Repositories

rules_nodejs produces several repositories for you to reference. Bazel represents your workspace as one repository, and code fetched or installed from outside your workspace lives in other repositories. These are referenced with the @repo// syntax in your BUILD files.

@nodejs

This repository is created by calling the node_repositories function in your WORKSPACE file. It contains the node, npm, and yarn programs.

As always, bazel query is useful for learning about what targets are available.

$ bazel query @nodejs//...
@nodejs//:node
...

You don’t typically need to reference the @nodejs repository from your BUILD files because it’s used behind the scenes to run node and fetch dependencies.

Some ways you can use this:

  • Run the Bazel-managed version of node: bazel run @nodejs//:node path/to/program.js
  • Run the Bazel-managed version of npm: bazel run @nodejs//:npm
  • Run the Bazel-managed version of yarn: bazel run @nodejs//:yarn
  • Install dependencies from nested package.json file(s) which were passed to node_repositories#package.json
    • using npm: bazel run @nodejs//:npm_node_repositories install
    • using yarn: bazel run @nodejs//:yarn_node_repositories

@npm

This repository is created by calling the npm_install or yarn_install function in your WORKSPACE file.

The name @npm is recommended in the simple case that you install only a single package.json file. If you have multiple, call the npm_install or yarn_install multiple times, and give each one a unique name. This results in multiple repositories, named whatever you chose, rather than “npm”. The following applies to any repository created by npm_install , or yarn_install, just replace @npm with the name you chose.

Again, use bazel query @npm//... to learn about all the targets declared in this repository.

Our philosophy is to mirror the installed npm dependencies in a way that’s idiomatic to reference them in Bazel.

Commonly used ones are:

  • Every file that was installed from npm: @npm//:node_modules. This target can have a very large number of files and slow down your build, however it’s a simple way to skip having to declare more fine-grained inputs to your BUILD targets.
  • If you had a dependency on the foo package, you can reference @npm//foo to get all the files. We mirror the npm dependency graph, so if foo declares a dependency on another package dep, Bazel will include that dependency when foo is used.
  • If the foo package has an executable program bar, then @npm//foo/bin:bar is a nodejs_binary that you can call with bazel run or can pass as the executable to your own rules.
  • Sometimes you need a UMD bundle, but a package doesn’t ship one. For example, the concatjs_devserver rule depends on third-party libraries having a named UMD entry point. The @npm//foo:foo__umd target will automatically run Browserify to convert the package’s main entry into UMD.

One convenient (maybe also confusing) way to understand what BUILD files are generated is to look at our integration test at https://github.com/bazelbuild/rules_nodejs/tree/stable/internal/npm_install/test/golden - this directory looks similar to the content of an @npm repository.

Generated macros for npm packages with bin entries

Any installed package that has one or more bin entries in the package.json get convenient macros generated. These are the Bazel equivalent of the ./node_modules/.bin/* files in your project which the package manager created.

For a package foo with some bin entries, we will create a .bzl file where you can load rules, at @npm//foo:index.bzl

If the foo package contains a bin entry bar, the index.bzl file will contain bar and bar_test macros. You can load these two generated rules in your BUILD file:

load("@npm//foo:index.bzl", "bar", "bar_test")

The bar macro can be called in two ways. If you pass outs or output_dir, it produces an npm_package_bin rule that invokes the tool to transform some inputs to outputs, useful as a dependency of another rule, or with bazel build. If you don’t pass outs or output_dir, then it will produce a nodejs_binary rule intended for use with bazel run. (The latter is identical to the @npm//foo/bin:bar target, just giving you a convenient way to alias it with a different label and pass it arguments).

See examples in rules_nodejs. A typical tool to use with outs is Babel, while a typical rule with no outputs is http_server.

The bar_test macro produces a nodejs_test that assumes the tool is a test runner, and produces a zero or one exit code, useful as a target with bazel test. See the examples of mocha_test in rules_nodejs.

You can also read https://dev.to/bazel/layering-in-bazel-for-web-389h to see an end-to-end example of using the generated bin macros.