Asset Minifier Bundle

A companion bundle for Symfony Asset Mapper that automatically minifies your JavaScript and CSS using esbuild — with no Node.js, no npm, and no build pipeline to configure.

Asset Mapper already handles import maps, cache-busting hashes, and ES module loading. This bundle completes the picture by shrinking your JS and CSS before they ship.

Why this bundle?

Symfony Asset Mapper is deliberately free of Node.js tooling. But without a minification step, your JavaScript and CSS ship as readable source — comments, whitespace, and verbose names included. This bundle fills that gap by running each JS and CSS file through esbuild at compile time, using a self-contained binary that PHP downloads and manages for you.

No package.json. No node_modules. No extra tooling to maintain.

What it minifies

• JavaScript — whitespace removal, comment stripping, identifier mangling, dead-code elimination
• CSS — whitespace removal, comment stripping, shorthand merging (e.g. margin-top/right/bottom/left → margin). Color values are intentionally preserved in their original format (rgba() stays rgba(), hsl() stays hsl()) to avoid browser compatibility issues with older targets
• Vendor assets are skipped in both cases — pre-minified packages from your importmap pass through untouched
• Works out of the box with symfonycasts/tailwind-bundle — Tailwind compiles first, then esbuild minifies the output

Requirements

• PHP 8.1+
• ext-phar and ext-zlib (enabled by default in standard PHP builds)
• Symfony 6.3, 7.x, or 8.x with symfony/asset-mapper

Installation

composer require halimjr/asset-minifier-bundle

Register the bundle in config/bundles.php:

return [
    // ...
    HalimJr\AssetMinifierBundle\AssetMinifierBundle::class => ['all' => true],
];

That's the entire setup. On the next php bin/console asset-map:compile, the esbuild binary is downloaded automatically and all your JavaScript and CSS assets are minified.

Benchmarks

Measured on a real Symfony application with 45 Stimulus controllers:

File	Original	Minified	Reduction
main_controller.js	66.8 KB	38.7 KB	42%
list_controller.js	27.1 KB	16.2 KB	40%
detail_controller.js	20.1 KB	11.8 KB	41%
sync_controller.js	16.2 KB	9.4 KB	42%
alert_controller.js	14.3 KB	8.5 KB	41%
Total (45 controllers)	419 KB	308 KB	~42%

Minification includes whitespace removal, comment stripping, and identifier mangling (local variable names shortened to single characters).

How it works

The bundle registers a compiler with Symfony Asset Mapper's pipeline via AssetCompilerInterface. During compilation, each JS and CSS file is piped through esbuild, which performs:

JavaScript (--minify --format=esm):

• Whitespace and comment removal
• Identifier mangling — local variable names are shortened to single characters
• Dead-code elimination — unreachable branches are removed

CSS (--minify --supported:hex-rgba=false):

• Whitespace and comment removal
• Shorthand merging — e.g. four margin-* declarations collapsed into one
• Color values preserved as authored — rgba() and hsl() are never converted to hex, avoiding compatibility issues with older browsers

The esbuild binary (~5 MB compressed) is downloaded once from the npm registry and cached in var/esbuild/. It is version-pinned by the bundle and re-downloaded automatically when you upgrade to a bundle version that ships a newer esbuild release.

Binary trust model. The download uses HTTPS with TLS peer verification (the same trust model as every npm install). Additionally, the bundle fetches the expected SHA-512 hash from the npm registry metadata API and verifies the tarball before extraction. If the hash does not match, the download is rejected and the binary is never written to disk.

Vendor assets are intentionally skipped. Pre-minified packages managed via importmap (e.g. @hotwired/stimulus, apexcharts) pass through untouched.

Stimulus controllers are safe. The bundle runs after Symfony's JavaScriptImportPathCompiler, so import paths are resolved and registered in the importmap before minification occurs. Method names used in data-action attributes are not mangled.

Tailwind CSS users. If you use symfonycasts/tailwind-bundle, it runs at a higher compiler priority than this bundle. Tailwind compiles your CSS first, and esbuild minifies the output. No configuration needed.

Configuration

No configuration is required for standard use. The following options are available if you need them:

# config/packages/asset_minifier.yaml
asset_minifier:
    esbuild_version: '0.25.2'  # pin to a specific esbuild version
    binary_path: null           # use a pre-existing binary instead of downloading
    source_maps: false          # set to true to embed inline source maps for production debugging
    minify_js: true             # set to false to skip JS minification
    minify_css: true            # set to false to skip CSS minification

Source maps

When source_maps: true, an inline source map is appended to each minified file. This lets you see original variable names and line numbers in browser DevTools, which is useful for debugging production issues without deploying unminified code.

Note that inline source maps increase file size. For most projects the trade-off is worth it in staging environments; in production, leave it disabled (the default).

binary_path is useful in environments where downloading from the npm registry is restricted, or when you manage the esbuild binary through your own provisioning (e.g. system packages, CI cache layers, Docker images).

Commands

Command	Description
asset-minifier:download	Downloads the esbuild binary for the current platform
asset-minifier:download --dry-run	Previews what would be downloaded without downloading

Deployment

GitHub Actions

- name: Install PHP dependencies
  run: composer install --no-dev --optimize-autoloader

- name: Download esbuild
  run: php bin/console asset-minifier:download

- name: Compile assets
  run: php bin/console asset-map:compile --env=prod

GitLab CI

deploy:
  script:
    - composer install --no-dev --optimize-autoloader
    - php bin/console asset-minifier:download
    - php bin/console asset-map:compile --env=prod
    - php bin/console cache:clear --env=prod

Docker

If your container's application directory is read-only, var/esbuild/ cannot be written at runtime. Download the binary during the image build step instead:

RUN composer install --no-dev --optimize-autoloader
RUN php bin/console asset-minifier:download --env=prod
RUN php bin/console asset-map:compile --env=prod

Alternatively, place the binary at a writable or pre-provisioned path and tell the bundle where it is:

# config/packages/prod/asset_minifier.yaml
asset_minifier:
    binary_path: /usr/local/bin/esbuild

When binary_path is set, the bundle uses that binary directly and never attempts a download.

General deploy script

composer install --no-dev --optimize-autoloader
php bin/console asset-minifier:download
php bin/console asset-map:compile --env=prod
php bin/console cache:clear --env=prod

The download command is idempotent — it does nothing if the correct binary version is already present. You can safely run it on every deploy.

Add the binary directory to .gitignore:

/var/esbuild/

Supported platforms

OS	x86_64	arm64
Linux	✓	✓
macOS	✓	✓
Windows	✓	✓

Contributing

Bug reports and pull requests are welcome at github.com/halimjr/asset-minifier-bundle.

License

MIT — see LICENSE.