Terser.md

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Terser rules for Bazel

The Terser rules run the Terser JS minifier with Bazel.

Wraps the Terser CLI documented at https://github.com/terser-js/terser#command-line-usage

Installation

Add the @bazel/terser npm package to your devDependencies in package.json.

Your WORKSPACE should declare a yarn_install or npm_install rule named npm. It should then install the rules found in the npm packages using the install_bazel_dependencies function. See https://github.com/bazelbuild/rules_nodejs/#quickstart

This causes the @bazel/terser package to be installed as a Bazel workspace named npm_bazel_terser.

Installing with self-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 terser:

# Create a terser rule to use in terser_minified#terser_bin
# attribute when using self-managed dependencies
nodejs_binary(
    name = "terser_bin",
    entry_point = "//:node_modules/terser/bin/uglifyjs",
    # Point bazel to your node_modules to find the entry point
    node_modules = ["//:node_modules"],
)

terser_minified

Run the terser minifier.

Typical example:

load("@npm_bazel_terser//:index.bzl", "terser_minified")

terser_minified(
    name = "out.min",
    src = "input.js",
    config_file = "terser_config.json",
)

Note that the name attribute determines what the resulting files will be called. So the example above will output out.min.js and out.min.js.map (since sourcemap defaults to true). If the input is a directory, then the output will also be a directory, named after the name attribute.

Usage

terser_minified(name, args, config_file, debug, sourcemap, src, terser_bin)

name

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

args

(List of strings): Additional command line arguments to pass to terser.

Terser only parses minify() args from the config file so additional arguments such as --comments may be passed to the rule using this attribute. See https://github.com/terser/terser#command-line-usage for the full list of terser CLI options.

Defaults to []

config_file

(label): A JSON file containing Terser minify() options.

This is the file you would pass to the --config-file argument in terser's CLI. https://github.com/terser-js/terser#minify-options documents the content of the file.

Bazel will make a copy of your config file, treating it as a template.

Run bazel with --subcommands to see the path to the copied file.

If you use the magic strings "bazel_debug" or "bazel_no_debug", these will be replaced with true and false respecting the value of the debug attribute or the --compilation_mode=dbg bazel flag.

For example,

{
    "compress": {
        "arrows": "bazel_no_debug"
    }
}

Will disable the arrows compression setting when debugging.

If config_file isn't supplied, Bazel will use a default config file.

Defaults to @npm_bazel_terser//:terser_config.default.json

debug

(Boolean): Configure terser to produce more readable output.

Instead of setting this attribute, consider using debugging compilation mode instead bazel build --compilation_mode=dbg //my/terser:target so that it only affects the current build.

Defaults to False

sourcemap

(Boolean): Whether to produce a .js.map output

Defaults to True

src

(label, mandatory): File(s) to minify.

Can be a .js file, a rule producing .js files as its default output, or a rule producing a directory of .js files.

Note that you can pass multiple files to terser, which it will bundle together. If you want to do this, you can pass a filegroup here.

terser_bin

(label): An executable target that runs Terser

Defaults to @npm_bazel_terser//:terser-local