Error [ERR_REQUIRE_ESM]: Must use import to load ES Module

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)

Affected packages and versions: latest

Steps to reproduce

Install in Node 10 environment (I haven’t tested on other node versions). Receive the following error:

Link to code example: https://github.com/googleapis/release-please/pull/870/checks?check_run_id=2390814891

Expected behavior

Library compiles.

I believe the goal is perhaps a dual-mode module (that would work for ESM and CJS?). This might just take some fiddling with extensions and export maps.

Here’s what we landed on for yargs:

https://github.com/yargs/yargs/blob/master/package.json#L5

It’s ugly but works on most Node versions.

Actual behavior

Error [ERR_REQUIRE_ESM]: Must use import to load ES Module: /home/runner/work/release-please/release-please/node_modules/unist-util-visit/index.js
require() of ES modules is not supported.
require() of /home/runner/work/release-please/release-please/node_modules/unist-util-visit/index.js from /home/runner/work/release-please/release-please/build/src/util/to-conventional-changelog-format.js is an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which defines all .js files in that package scope as ES modules.
Instead rename index.js to end in .cjs, change the requiring code to use import(), or remove "type": "module" from /home/runner/work/release-please/release-please/node_modules/unist-util-visit/package.json.

[wooorm]

• see the linked posts for more on this discussion and Next
• my experience maintaining dual esm/cjs is that there are tons of problems
• feel free to use the previous version while you or your tools are not ready

[johnrom]

Rollup is a bundler made for ESM. I don’t see why workarounds are needed to support ESM?

Workaround isn’t needed to support ESM, it’s used to support CJS consumers of a library built with rollup (or any bundler) (assuming they still exist out there in the world). I ran into this issue with an older Gatsby version that is otherwise working for now, for example.

Without this workaround, the cjs bundle will attempt to require the esm module upstream and receive this error.