How to determine if NPM package implements ES5 or ES6 modules?

Question

How to determine if NPM package supports ES5 or ES6 type of module ?

For node.js packages, just see whether they use the `.mjs` extension. You can also [look at the package.json](https://stackoverflow.com/q/42708484/1048572) — Bergi, Apr 30 '20 at 21:38
You can check this - https://www.npmjs.com/package/are-you-es5 — Kiran, Jun 17 '22 at 11:12

score 0 · Answer 1 · answered Apr 30 '20 at 21:32

This is a difficult question to answer with certainty, because it requires parsing JS -- a notoriously difficult problem.

If you're okay with a solution that gives the right answer most of the time -- I have a build system which transpiles ESMs with Babel in a mixed CommonJS/ESM environment with automatic dependency discovery. How I figure out if a given file is ESM or not is

egrep '^\s*import\s+.*\sfrom\s+' "$filename"

There are obvious situations where this will false-trigger, but it has served me well.

How to determine if NPM package implements ES5 or ES6 modules?

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