Export maps and node support

从 package.json 的 exports 和 main 字段，以及生成的 dist/index.modern.js 和 dist/index.js 开始；在 Node.js v14.15.3 下复现 require('color2k')。将 package 的 exports 解析与 Node 关于条件 exports 的文档进行比较。当已发布 package 的配置或输出能够通过 require() 加载，同时保留浏览器入口点时，即视为完成。

Hello there 👋,

I recently switched to microbundle for a bunch of my libs and I love it so far, however, I ran into an issue where the modern bundle (via exports) doesn't seem to run inside node.js.

My (simplified) package.json looks like this:

{
  "name": "color2k",
  "sideEffects": false,
  "exports": "./dist/index.modern.js",
  "main": "./dist/index.js",
  "unpkg": "./dist/index.umd.js",
  "module": "./dist/index.module.js",
  "source": "./src/index.ts",
  "types": "./dist/index.d.ts",
  "scripts": {
    "build": "microbundle"
  }
}

And after I run microbundle, my dist folder looks like this

index.d.ts
index.js
index.js.map
index.modern.js
index.modern.js.map
index.module.js
index.module.js.map
index.umd.js
index.umd.js.map

And after I publish with this config and run the following code with Node.js, I get the following error:

// my-file.js
const color2k = require('color2k');

// ...

SyntaxError: Unexpected token 'export'
    at wrapSafe (internal/modules/cjs/loader.js:979:16)
    at Module._compile (internal/modules/cjs/loader.js:1027:27)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Module.require (internal/modules/cjs/loader.js:952:19)
    at require (internal/modules/cjs/helpers.js:88:18)

I suspect this is due to Node.js not knowing what to do with exports. For more context, I'm not using the mjs extension when running this code in node LTS v14.15.3.

Maybe this is more of a question rather than a bug but in general: How do I use exports with microbundle? How can I author a package that is both for Node.js and browsers?

• Do I need to write a conditional exports map?
• Do I need to post-fix the modern bundle with the .mjs extension? If so how do I do that with microbundle?

Thanks for any support!

For now, I'll just remove the exports field.