Analysis of public NPM packages using the “module” field

npm-packages-module-field-analysis.md

I did some research into the package.json "module" field. I wrote some code to download all the the package.json files from all the public packages in the NPM registry. Here are some findings:

941 public NPM packages use the "module" field as of 2018-10-22.

Here are the top 30 packages, as ranked by number of public dependents (or see the full list):

Dependents	Package Name	"module" Field Value
16,286	should	./es6/should.js
15,472	sinon	./pkg/sinon-esm.js
1,641	redux	es/redux.js
1,579	rollup	dist/rollup.es.js
1,308	react-router	es/index.js
1,154	ramda	es/index.js
1,055	react-redux	es/index.js
1,023	rollup-plugin-babel	dist/rollup-plugin-babel.esm.js
845	vue	dist/vue.runtime.esm.js
810	d3	index.js
649	node-fetch	lib/index.mjs
637	rsvp	dist/rsvp.es.js
567	redux-thunk	es/index.js
560	history	es/index.js
469	whatwg-fetch	./fetch.js
463	rxjs	./_esm5/index.js
410	react-bootstrap	es/index.js
404	acorn	dist/acorn.mjs
390	rollup-plugin-commonjs	dist/rollup-plugin-commonjs.es.js
331	deepmerge	dist/es.js
314	firebase	dist/index.esm.js
248	material-ui	./index.es.js
239	pouchdb	./lib/index.es.js
236	graphql	index.mjs
235	lolex	./lolex.js
234	precss	index.js
210	angular-ui-router	lib-esm/index.js
203	three	build/three.module.js
181	bignumber.js	bignumber.mjs
174	radium	es/index.js

Some of these packages, like should and sinon and redux and vue and d3, surely have huge numbers of private dependents not reflected in the totals above.

Of the 941 packages that use "module", here are some numbers about file extensions:

• 783 packages point directly to a .js file.
• 75 packages point directly to an .mjs file.
• 83 packages point to a filename with an implied (or no) extension, or a folder name.

Of the 858 packages that point directly to a .js or .mjs file, 274 point directly to files that use “multi-dot” file extensions:

• 133 use .es.js
• 84 use .esm.js
• 13 use .es.mjs
• 11 use .module.js
• 10 use .es6.js
• 7 use .m.js
• 5 use .es5.js
• 4 use .min.js
• 2 use .next.js
• 2 use .es2015.js
• 1 each use .esm.js, .es8.js, .ems.js

Of the 83 packages that have "module" values that don’t end in .js or .mjs, most appear to point to files with an automatically-added extension (e.g. index):

• 57 use index
• 6 use es
• 4 use dist
• 2 use main
• 1 each use components, Animate, DialogWrap, src, dist-es6, hashids-esm, module, vdt.esm, immupdate, immutable, esm, esmodule, Booth, please-wait, form-urlencoded

Collectively, the 941 packages using the "module" field have 41,226 public dependents (inclusive of duplicates, e.g. packages that depend on more than one "module"-using package).

Reading through the full list of public packages using "module", many appear to be related to the React, Vue and D3 ecosystems.

This is very impressive work... vital for decisions ahead 👍