Building JavaScript Outputs
Bazel supports an incremental and customizable means of building and testing JavaScript outputs from JavaScript, TypeScript, and Angular sources.
Note: This document describes Bazel features and workflows that are useful, but the Bazel team has not fully verified and does not officially support these features and workflows.
Contents
- Overview
- Setting up your environment
- Building JavaScript inputs
- Building TypeScript inputs
- Building Angular inputs
Overview
Bazel rules for building JavaScript outputs are split into three layers, since you can use JavaScript without TypeScript, and TypeScript without Angular. This document assumes you are already familiar with Bazel and uses the Angular for Bazel sample project to illustrate the recommended configuration. You can use the sample project as a starting point and add your own code to it to start building with Bazel.
If you’re new to Bazel, take a look at the “Getting Started” material before proceeding.
Setting up your environment
To set up your environment for building JavaScript outputs with Bazel, do the following:
Step 1: Installing Bazel
If you have not already done so, Install Bazel.
Step 2: Installing iBazel
iBazel, or iterative Bazel, is a “watchdog” version of Bazel that automatically runs whenever your source files change. Use it to auto-run your tests and auto-refresh the code served by the development server.
Install iBazel globally using your package manager of choice. The global installation is required so that iBazel is in your PATH variable. Also install a specific version of iBazel into your project so that your whole team updates together. For example:
npm install --save-dev @bazel/ibazel
npm install --global @bazel/ibazel
or
yarn add -D @bazel/ibazel
yarn global add @bazel/ibazel
To use ibazel
, simply replace bazel
with ibazel
in your Bazel commands.
Step 3: Configuring the bazel.rc
file
Any Bazel build flag or option that can be placed on the command line can also
be set in the project’s bazel.rc
file
so that it is applied every time Bazel builds or tests the project.
Based on how you want to share Bazel settings across your project and team(s), you can use any combination of the following techniques:
-
To use the same Bazel settings for the project, create a
tools/bazel.rc
file at the root of the Bazel workspace. Adding it to the workspace will check the file into version control and propagate it to others working on the project as well as the CI system. -
To personalize Bazel settings for the project but not share them, create a
.bazel.rc
file at the root of the project and add the file to your.gitignore
list. -
To personalize Bazel settings for all of your projects on your local machine, create a
.bazel.rc
file in your home directory.
Here’s an example tools/bazel.rc
file to share with your team. Modify this
template as needed.
###############################
# Directory structure #
###############################
# Globally cache downloaded artifacts.
build --experimental_repository_cache=~/.bazel_cache/
test --experimental_repository_cache=~/.bazel_cache/
run --experimental_repository_cache=~/.bazel_cache/
# Don't create bazel-* symlinks in the WORKSPACE directory. These
# symlinks require .gitignore and may scare users. Instead, run
# `bazel info bazel-bin` to find out where the outputs are stored.
build --symlink_prefix=/
# Another good choice is to create a dist/ directory. Then you can
# use build --symlink_prefix=dist/ to get folders like dist/bin.
# Be aware that this setup will still create a bazel-out symlink in
# your project directory, which you may need to exclude from the
# editor's search path.
###############################
# Output #
###############################
# A more useful default output mode for bazel query, which
# prints "ng_module rule //foo:bar" instead of just "//foo:bar".
query --output=label_kind
# By default, failing tests don't print any output, it's logged to a
# file instead.
test --test_output=errors
# Show which actions are running under which workers and print all
# the actions running in parallel. This shows that Bazel runs on all
# cores of a CPU.
build --experimental_ui
test --experimental_ui
###############################
# Typescript / Angular / Sass #
###############################
# Make TypeScript and Angular compilation fast, by keeping a few
# copies of the compiler running as daemons, and cache SourceFile
# ASTs to reduce parse time.
build --strategy=TypeScriptCompile=worker --strategy=AngularTemplateCompile=worker
# Enable debugging tests with --config=debug
test:debug --test_arg=--node_options=--inspect-brk --test_output=streamed --test_strategy=exclusive --test_timeout=9999 --nocache_test_results
Step 4: (Optional) Setting up Continuous Integration (CI)
For building JavaScript outputs with Bazel in a CI setting, it’s useful to use a container as the environment. The ngcontainer Docker image is a ready-to-use environment you can use that makes your builds reproducible in other environments, such as your local machine. This reproducibility is especially convenient on CircleCI, which lets you choose a Docker image as the environment for your build. See the example CircleCI configuration in the sample project to learn more.
Tip: When building in a CI environment, add settings to your bazel.rc
file
that are specific to CI using the build:ci
and or test:ci
prefixes. With
this configuration, you can enable those CI-specific options by simply adding
the --config=ci
argument to your Bazel/iBazel commands.
Building JavaScript
Use the rules_nodejs
rules to build NodeJS applications and execute JavaScript code within Bazel. You
can execute JavaScript tools in the Bazel toolchain, binary programs, or tests.
The NodeJS rules add the NodeJS runtime to your Bazel project.
Most notable NodeJS rules include:
-
nodejs_binary
- builds an executable program based on JavaScript source files and an entry point path relative to the output root. To provide extra inputs to be read at runtime, put them in the data attribute. -
jasmine_node_test
- runs JavaScript spec files through the Jasmine test framework. See the node_js API documentation for more information.
Building TypeScript
Use the rules_typescript
rules to build JavaScript outputs from TypeScript inputs.
To set up your Bazel project for building TypeScript inputs, do the following:
-
Make Bazel aware of the TypeScript build rules by adding the following entry to your
WORKSPACE
file:http_archive( name = "build_bazel_rules_typescript", url = "https://github.com/bazelbuild/rules_typescript/archive/v0.13.0.zip", strip_prefix = "rules_typescript-0.13.0", ) load("@build_bazel_rules_typescript//:defs.bzl", "ts_setup_workspace") ts_setup_workspace()
-
Add the
--strategy
settings to yourbazel.rc
file as shown in the example.bazel.rc
file in “Configuring the bazel.rc file”.
Compiling TypeScript inputs (ts_library
)
The ts_library
rule compiles one package of TypeScript code at a time. Each
library compiles independently using the .d.ts
declaration files from its
dependencies. Thus, Bazel will only rebuild a package if the API the package
depends on changes.
The ts_library
rule, by default, outputs a .d.ts
file for each .ts
source
file input into it, plus an ES5 (devmode) .js
file to be used as inputs for
rule targets that depend on the current target, including transitively.
Tip: You can try out the ts_library
rule by running bazel build src in
the sample project.
Note: We recommend standardizing your TypeScript settings into a single
tsconfig.json
file or as few tsconfig.json
files as possible.
Note the following:
-
Bazel controls parts of the
tsconfig.json
file that define locations of input and output files, manage dependencies on typings, and produce JavaScript output that’s readable by downstream tooling. Currently, this format is unbundled UMD modules, wrapping noth named (non-anonymous) AMD modules andcommonjs
modules. -
Bazel may introduce new requirements for your TypeScript code. For example, Bazel uses the
-declarations
flag to produce.d.ts
outputs required by dependent rule targets; your code may require adjustment to not produce errors when the-declarations
flag is in use. -
If your TypeScript builds are slow, consider granularizing the affected rule target(s) into smaller sub-targets and declaring dependencies between them appropriately.
Running a development server (ts_devserver
)
The ts_devserver
rule brings up a development server from your application
sources. It’s intended for use with the ibazel run
command so that the server
picks up your code changes immediately. The rule injects a livereload
script
into the browser, which causes the page to auto-refresh with the latest changes
at the completion of each build.
Tip: You can test-drive the development server feature by running
ibazel run src: devserver
on the sample project.
Testing TypeScript code (ts_web_test
)
Use the ts_web_test
rule to execute the Karma test runner. This rule works
best with ibazel so that both the test runner and the browser pick up your
changes at the completion of each build. For faster builds, Bazel bundles your
code and its dependencies into a single JavaScript file delivered to the browser
when the test runner executes.
If you need to match lots of tests with a target pattern such as bazel test //…
or using CI, run the ts_web_test
rule with the regular bazel test
command
instead. Bazel will then launch a headless Chrome instance and exit after a
single run.
Tip: You can test-drive the ts_web_test
rule by running ibazel run
or
bazel run
on the src/hello-world:test
target in the sample project.
Building Angular inputs
Bazel can build JavaScript outputs from Angular. For instructions, see Building Angular with Bazel.