Simple conditions flag

[guybedford]

Since the PR for a --dev flag got stalled at nodejs/node#33171 it could still be useful to provide a top-level way to set Node.js conditions like "development" and "production".

The simplest proposal then would just be to have a top-level --conditions flag:

node --conditions=production,custom x.js

as a comma-separated list of conditions to add to the resolution process.

Perhaps if there is time to discuss this today we can get some feedback before any PR work is attempted.

[jkrems]

I assume the idea would be that they would be similar to "node" and apply to all import and require resolutions?

[bmeck]

@jkrems that brings up a good point about prohibiting some values from the CLI

[ljharb]

Would these conditions select for CJS, or ESM? Some folks might but CJS in production, and some might put ESM in production; some users may prefer ESM and some may prefer CJS.

[bmeck]

@ljharb I'm not sure I understand the question / workflow

[ljharb]

So, pre-ESM, the "browser" field was "CJS meant to be bundled for the browser", and "main" was "CJS meant to be required by node".

In conditions, "require" is for "CJS" and "import" is for "ESM". Which module system is "production" for?

[bmeck]

ljharb: it isn't for a module system, it is for a differing implementation; e.g. load the module with debugging hooks exposed vs not

[ljharb]

@bmeck right, but load the module as ESM, or as CJS?

[bmeck]

@ljharb thats unrelated to even require or import, those conditions are just the means by which it was loaded.

[jkrems]

@ljharb Conditions can (and in this case likely should) be combined. E.g.:

"exports": {
  "import": { "development": "./dev.mjs", "default": "./prod.mjs" },
  "require": { "development": "./dev.cjs", "default": "./prod.cjs" }
}

[ljharb]

@jkrems now that makes sense to me. Is there even a use case for using dev/prod on the first level of exports, as opposed to the second as you illustrated?

[jkrems]

Depending on how terse you want to be, it can be handy to use it top-level like this:

"exports": {
  "require": { "development": "./dev.cjs", "default": "./prod.cjs" },
  "development": "./dev.mjs",
  "default": "./prod.mjs"
}

[bmeck]

You also might have modules you never want to use in production, so top level would be "development"