Why do bundlers import module fields but don't transpile by default?

1. By default bundlers resolve a packages import from the module field over the main in package.json (webpack and rollup, for example) which points to a projects ES6 module entry.

2. By default bundlers ignore transformations on anything from node_modules.

Aren't these two behaviors contradictory?

There are solutions to this:

• Change the mainFields option to import main before module.
• Change your exclude option to transpile specific package(s).
• Use an es-check and only transpile packages that need it.

But yeah, this has always confused me. Am I missing something? Why do they do this?

Comments

[Jordi]

Well, sometimes you want to bundle but don't want to transpile. The best thing about webpack is that you can configure it however you like.

[Sebastian Nitu]

Yeah, totally. I love webpack too and have found ways to configure a bundle and resolve the issue in both webpack and rollup. I guess my general question is why does it act this way by default? It feels very counter-intuitive and while I was searching for solutions I noticed A LOT of similar posts of people trying to resolve that same issue.