@bazel/concatjs

Concatjs is a JavaScript bundler, in a trivial sense: the UNIX cat command is a basic implementation:

$ cat one.js two.js > bundle.js

Clearly self-evident is that this bundler is super-fast and simple. A performant implementation adds some in-memory caching, and for developer ergonomics you add a simple IIFE wrapper around each file so that the Chrome DevTools shows the files in the tree as if they had been independently loaded.

However at its core, concatjs requires a big tradeoff of a migration cost to buy-in, to get this incredible performance. The path of the JavaScript files is lost in the bundling process, so they must contain their module ID internally.

Named AMD/UMD modules and goog.module are the two JS module formats that are compatible with concatjs. Most packages do not ship with this format, so in order to use concatjs tooling, you have to shim your code and dependencies. See the Compatibility section below.

This is at the core of how Google does JavaScript development. So Bazel rules that originated in Google's codebase have affordances for concatjs. For example ts_library produces named AMD modules in its "devmode" output, and karma_web_test expects to bundle inputs using concatjs.

Compatibility

First-party code

First-party code has to be authored as named AMD/UMD modules. This is also historically referred to as "RequireJS" modules since that's the JS loader that is typically used with them.

If you write TypeScript, you can do this following their documentation.

There is an example in this repository: we have an index.ts file that wants to be used with require.js require("@bazel/concatjs"). So it declares that module name using the TS triple-slash syntax:

///<amd-module name="@bazel/concatjs"/>

it is also compiled with the "compilerOptions": { "module": "umd" } TypeScript setting.

Third-party code

To make it easier to produce a UMD version of a third-party npm package, we automatically generate a target that uses Browserify to build one, using the main entry from the package's package.json. In most cases this will make the package loadable under concatjs. This target has a __umd suffix. For example, if your library is at @npm//foo then the UMD target is @npm//foo:foo__umd.

An example where this fixes a users issue: https://github.com/bazelbuild/rules_nodejs/issues/2317#issuecomment-735921318

In some cases, the generated UMD bundle is not sufficient, and in others it fails to build because it requires some special Browserify configuration. You can always write your own shim that grabs a symbol from a package you use, and exposes it in an AMD/require.js-compatible way. For example, even though RxJS ships with a UMD bundle, it contains multiple entry points and uses anonymous modules, not named modules. So our Angular/concatjs example has a rxjs_shims.js file that exposes some RxJS operators, then at https://github.com/bazelbuild/rules_nodejs/blob/2.3.1/examples/angular/src/BUILD.bazel#L65-L71 this is combined in a filegroup with the rxjs.umd.js file. Now we use this filegroup target when depending on RxJS in a concatjs_* rule.

Ultimately by using concatjs, you're signing up for at least a superficial understanding of these shims and may need to update them when you change your dependencies.

Serving JS in development mode under Bazel

There are two choices for development mode:

1. Use the concatjs_devserver rule to bring up our simple, fast development server. This is intentionally very simple, to help you get started quickly. However, since there are many development servers available, we do not want to mirror their features in yet another server we maintain.
2. Teach your real frontend server to serve files from Bazel's output directory. This is not yet documented. Choose this option if you have an existing server used in development mode, or if your requirements exceed what the concatjs_devserver supports. Be careful that your development round-trip stays fast (should be under two seconds).

To use concatjs_devserver, you simply load the rule, and call it with deps that point to your ts_library target(s):

load("@npm//@bazel/concatjs:index.bzl", "concatjs_devserver", "ts_library")

ts_library(
    name = "app",
    srcs = ["app.ts"],
)

concatjs_devserver(
    name = "devserver",
    # We'll collect all the devmode JS sources from these TypeScript libraries
    deps = [":app"],
    # This is the path we'll request from the browser, see index.html
    serving_path = "/bundle.js",
    # The devserver can serve our static files too
    static_files = ["index.html"],
)

The index.html should be the same one you use for production, and it should load the JavaScript bundle from the path indicated in serving_path.

If you don't have an index.html file, a simple one will be generated by the concatjs_devserver.

See examples/app in this repository for a working example. To run the devserver, we recommend you use ibazel:

$ ibazel run examples/app:devserver

ibazel will keep the devserver program running, and provides a LiveReload server so the browser refreshes the application automatically when each build finishes.

Testing with Karma

The karma_web_test rule runs karma tests with Bazel.

It depends on rules_webtesting, so you need to add this to your WORKSPACE if you use the web testing rules in @bazel/concatjs:

# Fetch transitive Bazel dependencies of karma_web_test
http_archive(
    name = "io_bazel_rules_webtesting",
    sha256 = "e9abb7658b6a129740c0b3ef6f5a2370864e102a5ba5ffca2cea565829ed825a",
    urls = ["https://github.com/bazelbuild/rules_webtesting/releases/download/0.3.5/rules_webtesting.tar.gz"],
)

# Set up web testing, choose browsers we can test on
load("@io_bazel_rules_webtesting//web:repositories.bzl", "web_test_repositories")

web_test_repositories()

load("@io_bazel_rules_webtesting//web/versioned:browsers-0.3.3.bzl", "browser_repositories")

browser_repositories(
    chromium = True,
    firefox = True,
)

Known issues with running Chromium for macOS/Windows in Bazel

For macOS and Windows, Chromium comes with files that contain spaces in their file names. This breaks runfile tree creation within Bazel due to a bug. There are various workarounds that allow for Chromium on these platforms:

• Instruct Bazel to automatically disable runfile tree creation if not needed. More details here
• Instruct Bazel to use an alternative experimental approach for creating runfile trees. More details here

Installing with user-managed dependencies

If you didn't use the yarn_install or npm_install rule to create an npm workspace, you'll have to declare a rule in your root BUILD.bazel file to execute karma:

# Create a karma rule to use in karma_web_test_suite karma
# attribute when using user-managed dependencies
nodejs_binary(
    name = "karma/karma",
    entry_point = "//:node_modules/karma/bin/karma",
    # Point bazel to your node_modules to find the entry point
    data = ["//:node_modules"],
)

concatjs_devserver

USAGE

concatjs_devserver is a simple development server intended for a quick "getting started" experience.

Additional documentation here

ATTRIBUTES

(Name, mandatory): A unique name for this target.

(List of strings): Additional root paths to serve static_files from. Paths should include the workspace name such as ["__main__/resources"]

Defaults to []

(List of labels): Scripts to include in the JS bundle before the module loader (require.js)

Defaults to []

(List of labels): Targets that produce JavaScript, such as ts_library

Defaults to []

(Label): Go based devserver executable.

        With cross-platform RBE for OSX & Windows ctx.executable.devserver will be linux as --cpu and
        --host_cpu must be overridden to k8. However, we still want to be able to run the devserver on the host
        machine so we need to include the host devserver binary, which is ctx.executable.devserver_host, in the
        runfiles. For non-RBE and for RBE with a linux host, ctx.executable.devserver & ctx.executable.devserver_host
        will be the same binary.

        Defaults to precompiled go binary setup by @bazel/typescript npm package

Defaults to @npm//@bazel/concatjs/devserver:devserver

(Label): Go based devserver executable for the host platform. Defaults to precompiled go binary setup by @bazel/typescript npm package

Defaults to @npm//@bazel/concatjs/devserver:devserver

(String): The entry_module should be the AMD module name of the entry module such as "__main__/src/index". concatjs_devserver concats the following snippet after the bundle to load the application: require(["entry_module"]);

Defaults to ""

(Integer): The port that the devserver will listen on.

Defaults to 5432

(List of labels): User scripts to include in the JS bundle before the application sources

Defaults to []

(String): The path you can request from the client HTML which serves the JavaScript bundle. If you don't specify one, the JavaScript can be loaded at /_/ts_scripts.js

Defaults to "/_/ts_scripts.js"

(List of labels): Arbitrary files which to be served, such as index.html. They are served relative to the package where this rule is declared.

Defaults to []

ts_library

USAGE

type-check and compile a set of TypeScript sources to JavaScript.

It produces declarations files (.d.ts) which are used for compiling downstream TypeScript targets and JavaScript for the browser and Closure compiler.

By default, ts_library uses the tsconfig.json file in the workspace root directory. See the notes about the tsconfig attribute below.

Serving TypeScript for development

ts_library is typically served by the concatjs_devserver rule, documented in the @bazel/concatjs package.

Accessing JavaScript outputs

The default output of the ts_library rule is the .d.ts files. This is for a couple reasons:

• help ensure that downstream rules which access default outputs will not require a cascading re-build when only the implementation changes but not the types
• make you think about whether you want the devmode (named UMD) or prodmode outputs

You can access the JS output by adding a filegroup rule after the ts_library, for example

ts_library(
    name = "compile",
    srcs = ["thing.ts"],
)

filegroup(
    name = "thing.js",
    srcs = ["compile"],
    # Change to es6_sources to get the 'prodmode' JS
    output_group = "es5_sources",
)

my_rule(
    name = "uses_js",
    deps = ["thing.js"],
)

ATTRIBUTES

(Name, mandatory): A unique name for this target.

(List of labels): Additional files the Angular compiler will need to read as inputs. Includes .css and .html files

Defaults to []

(Label): Sets a different TypeScript compiler binary to use for this library. For example, we use the vanilla TypeScript tsc.js for bootstrapping, and Angular compilations can replace this with ngc.

The default ts_library compiler depends on the //@bazel/typescript target which is setup for projects that use bazel managed npm deps and install the @bazel/typescript npm package.

You can also use a custom compiler to increase the NodeJS heap size used for compilations.

To do this, declare your own binary for running tsc_wrapped, e.g.:

nodejs_binary(
    name = "tsc_wrapped_bin",
    entry_point = "@npm//:node_modules/@bazel/typescript/internal/tsc_wrapped/tsc_wrapped.js",
    templated_args = [
        "--node_options=--max-old-space-size=2048",
    ],
    data = [
        "@npm//protobufjs",
        "@npm//source-map-support",
        "@npm//tsutils",
        "@npm//typescript",
        "@npm//@bazel/typescript",
    ],
)

then refer to that target in the compiler attribute.

Note that nodejs_binary targets generated by npm_install/yarn_install can include data dependencies on packages which aren't declared as dependencies. For example, if you use tsickle to generate Closure Compiler-compatible JS, then it needs to be a data dependency of tsc_wrapped so that it can be loaded at runtime.

Defaults to @npm//@bazel/concatjs/internal:tsc_wrapped_bin

(List of labels)

Defaults to []

(List of labels): Compile-time dependencies, typically other ts_library targets

Defaults to []

(String): Set the typescript module compiler option for devmode output.

This value will override the module option in the user supplied tsconfig.

Defaults to "umd"

(String): Set the typescript target compiler option for devmode output.

This value will override the target option in the user supplied tsconfig.

Defaults to "es2015"

(List of strings)

Defaults to []

(Boolean)

Defaults to True

(Boolean): Testing only, whether to type check inputs that aren't srcs.

Defaults to False

(Boolean): Link the workspace root to the bin_dir to support absolute requires like 'my_wksp/path/to/file'.

If source files need to be required then they can be copied to the bin_dir with copy_to_bin.

Defaults to False

(String)

Defaults to ""

(String)

Defaults to ""

(String): The package name that the linker will link this ts_library output as.

If package_path is set, the linker will link this package under <package_path>/node_modules/<package_name>. If package_path is not set the this will be the root node_modules of the workspace.

Defaults to ""

(String): The package path in the workspace that the linker will link this ts_library output to.

If package_path is set, the linker will link this package under <package_path>/node_modules/<package_name>. If package_path is not set the this will be the root node_modules of the workspace.

Defaults to ""

(String): Set the typescript module compiler option for prodmode output.

This value will override the module option in the user supplied tsconfig.

Defaults to "esnext"

(String): Set the typescript target compiler option for prodmode output.

This value will override the target option in the user supplied tsconfig.

Defaults to "es2015"

(String)

Defaults to "browser"

(List of labels) The dependencies of this attribute must provide: JsInfo

Defaults to []

(List of labels, mandatory): The TypeScript source files to compile.

(Boolean): Intended for internal use only.

Allows you to disable the Bazel Worker strategy for this library. Typically used together with the "compiler" setting when using a non-worker aware compiler binary.

Defaults to True

(Label): A tsconfig.json file containing settings for TypeScript compilation. Note that some properties in the tsconfig are governed by Bazel and will be overridden, such as target and module.

The default value is set to //:tsconfig.json by a macro. This means you must either:

• Have your tsconfig.json file in the workspace root directory
• Use an alias in the root BUILD.bazel file to point to the location of tsconfig: alias(name="tsconfig.json", actual="//path/to:tsconfig-something.json") and also make the tsconfig.json file visible to other Bazel packages: exports_files(["tsconfig.json"], visibility = ["//visibility:public"])
• Give an explicit tsconfig attribute to all ts_library targets

Defaults to None

(Boolean): If using tsickle, instruct it to translate types to ClosureJS format

Defaults to True

(Boolean): Run the Angular ngtsc compiler under ts_library

Defaults to False

karma_web_test

USAGE

Runs unit tests in a browser with Karma.

When executed under bazel test, this uses a headless browser for speed. This is also because bazel test allows multiple targets to be tested together, and we don't want to open a Chrome window on your machine for each one. Also, under bazel test the test will execute and immediately terminate.

Running under ibazel test gives you a "watch mode" for your tests. The rule is optimized for this case - the test runner server will stay running and just re-serve the up-to-date JavaScript source bundle.

To debug a single test target, run it with bazel run instead. This will open a browser window on your computer. Also you can use any other browser by opening the URL printed when the test starts up. The test will remain running until you cancel the bazel run command.

This rule will use your system Chrome by default. In the default case, your environment must specify CHROME_BIN so that the rule will know which Chrome binary to run. Other browsers and customLaunchers may be set using the a base Karma configuration specified in the config_file attribute.

By default we open a headless Chrome. To use a real Chrome browser window, you can pass --define DISPLAY=true to Bazel, along with configuration_env_vars = ["DISPLAY"] on karma_web_test.

PARAMETERS

A list of JavaScript test files

Defaults to []

Other targets which produce JavaScript such as ts_library

Defaults to []

Runtime dependencies

Defaults to []

Pass these configuration environment variables to the resulting binary. Chooses a subset of the configuration environment variables (taken from ctx.var), which also includes anything specified via the --define flag. Note, this can lead to different outputs produced by this rule.

Defaults to []

JavaScript files to include before the module loader (require.js). For example, you can include Reflect,js for TypeScript decorator metadata reflection, or UMD bundles for third-party libraries.

Defaults to []

Dependencies which should be loaded after the module loader but before the srcs and deps. These should be a list of targets which produce JavaScript such as ts_library. The files will be loaded in the same order they are declared by that rule.

Defaults to []

Arbitrary files which are available to be served on request. Files are served at: /base/<WORKSPACE_NAME>/<path-to-file>, e.g. /base/npm_bazel_typescript/examples/testing/static_script.js

Defaults to []

User supplied Karma configuration file. Bazel will override certain attributes of this configuration file. Attributes that are overridden will be outputted to the test log.

Defaults to None

Standard Bazel tags, this macro adds tags for ibazel support

Defaults to []

list of peer npm deps required by karma_web_test

Defaults to ["@npm//karma", "@npm//karma-chrome-launcher", "@npm//karma-firefox-launcher", "@npm//karma-jasmine", "@npm//karma-requirejs", "@npm//karma-sourcemap-loader", "@npm//requirejs"]

Passed through to karma_web_test

karma_web_test_suite

USAGE

Defines a test_suite of web_test targets that wrap a karma_web_test target.

This macro accepts all parameters in karma_web_test and adds additional parameters for the suite. See karma_web_test docs for all karma_web_test.

The wrapping macro is web_test_suite which comes from rules_websting: https://github.com/bazelbuild/rules_webtesting/blob/master/web/web.bzl.

PARAMETERS

The base name of the test

A sequence of labels specifying the browsers to use.

Defaults to None

Data dependencies for the wrapper web_test targets.

Defaults to []

A list of test tag strings to use for the wrapped karma_web_test target.

Defaults to ["manual", "noci"]

Arguments for the wrapped karma_web_test target.