esbuild is unable to tree-shake rxjs under node platform

[benlesh]

Discussed in #6785

^{Originally posted by Conaclos January 28, 2022}
Hi!

I discovered that esbuild is not able to tree-shake rxjs package when bundling under node platform.
esbuild priorizes exports condition 'node' over main-fields.

Demonstration

$ cat index.js
export { Subject } from 'rxjs'

$ esbuild --bundle index.js --platform=node | wc -l
9654

$ # Specifying main-fields does not change the output
$ esbuild --bundle index.js --platform=node --main-fields=es2015,module,main | wc -l
9654

$ # browser bundle is lighter
$ esbuild --bundle index.js --platform=browser | wc -l
1161

Note that we need to bundle for node since our project and most of our dependencies imports node-specific modules.

How to solve the issue?

rxjs should not use the condition "node".
It should use the condition "require":

  ...
  "exports": {
    ".": {
      "require": "./dist/cjs/index.js",
      "es2015": ...,
      "default": ...
    },
    ....

instead of:

  ...
  "exports": {
    ".": {
      "node": "./dist/cjs/index.js",
      "es2015": ...,
      "default": ...
    },
    ....
```</div>

[akanass]

I guess it's related to my one year issue

[benlesh]

@akanass Yes. I know that's a "one year issue". Unfortunately, RxJS is so widely used that if we pushed out breaking changes and published new majors too often it would cause a lot of churn for everyone. That will be fixed in 8.x

[akanass]

@benlesh yes I know that :) but when I saw your issue I have remembered my issue that's why I mentioned it to be sure to cover all points