Vendoring

Minifying

Run a download through bun, esbuild or terser before it lands in vendor/javascript.

Why#

Plenty of packages publish unminified ESM (pdfjs-dist, choices.js, luxon), and a CDN that serves package files hands them out as published. Lighthouse's unminified-JavaScript audit will tell you which of your vendored packages those are.

pin --minify#

$ ./bin/importmap pin luxon --minify
Pinning "luxon" to vendor/javascript/luxon.js via download from https://ga.jspm.io/npm:[email protected]/build/es6/luxon.mjs (minified)

The first of bun, esbuild or terser found in node_modules/.bin or on your PATH (Windows .cmd shims included) is used, always in transform-only mode so bare import specifiers are left exactly as the CDN resolved them and the import map keeps resolving them.

The pin records it, and so does the header of the vendored file:

config/importmap.rb

pin "luxon" # @3.7.2 (minified)
pin "stimulus-use" # @0.53.1 (esm.run, minified)

From then on update, pristine and a plain pin keep minifying that package; --no-minify turns it off again. Dependencies pinned alongside a --minify download are minified too.

Everything already vendored#

pristine redownloads every vendored package; with --minify it minifies them all in one go and records it on each pin:

./bin/importmap pristine --minify

Bringing your own minifier#

Assign anything that responds to call(source) and returns the minified source. bin/importmap loads config/application.rb but not your initializers, so the assignment has to happen there (or in a file it requires):

config/application.rb

require "importmap/packager"

Importmap::Packager.minifier = ->(source) { MyMinifier.minify(source) }