Unable to resolve subpath exports

[IanVS]

This one is confusing me. I'm trying to import from msw/browser (using msw@next), but getting this error when I try to build using tsup:

ESM Build start
✘ [ERROR] Could not resolve "msw/browser"

    lib/msw-config.ts:2:46:
      2 │ import { setupWorker, type SetupWorker } from 'msw/browser';
        ╵                                               ~~~~~~~~~~~~~

  The path "./browser" is not exported by package "msw":

    node_modules/msw/package.json:8:13:
      8 │   "exports": {
        ╵              ^

  The file "./lib/browser/index.mjs" is exported at path "./browser":

    node_modules/msw/package.json:19:16:
      19 │       "import": "./lib/browser/index.mjs",
         ╵                 ~~~~~~~~~~~~~~~~~~~~~~~~~

  Import from "msw/browser" to get the file "node_modules/msw/lib/browser/index.mjs":

    lib/msw-config.ts:2:46:
      2 │ import { setupWorker, type SetupWorker } from 'msw/browser';
        │                                               ~~~~~~~~~~~~~
        ╵                                               "msw/browser"

  You can mark the path "msw/browser" as external to exclude it from the bundle, which will remove
  this error.

ESM Build failed
Error: Build failed with 1 error:
lib/msw-config.ts:2:46: ERROR: Could not resolve "msw/browser"

I'm using the latest tsup version, and you can see where this is happening here in this PR: miragejs/mirage-msw#12.

And, here is the package.json of msw, which shows the ./browser export: https://github.com/mswjs/msw/blob/bb02e57568e052206ed8bc55b800cad5fc4c8c78/package.json#L16C8-L22

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[IanVS]

Oh I see, this is coming from esbuild, and matches the behavior of node, because of the "node": null, condition.

"./browser": {
      "node": null,
      "types": "./lib/browser/index.d.ts",
      "require": "./lib/browser/index.js",
      "import": "./lib/browser/index.mjs",
      "default": "./lib/browser/index.js"
    },

I would have thought the ESM build would use the import condition, but I guess not since the "node" condition comes first?

[IanVS]

Alright, passing --platform browser solves it. I didn't realize TSUP by default sends platform: node to esbuild, which causes it to consider the node export condition.