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doc: clarify conditional exports guidance
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PR-URL: #34306
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Jan Krems <jan.krems@gmail.com>
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guybedford authored and MylesBorins committed Jul 16, 2020
1 parent 1dd2653 commit 17174e6
Showing 1 changed file with 13 additions and 5 deletions.
18 changes: 13 additions & 5 deletions doc/api/esm.md
Original file line number Diff line number Diff line change
Expand Up @@ -456,16 +456,24 @@ Conditional exports can also be extended to exports subpaths, for example:
"exports": {
".": "./main.js",
"./feature": {
"browser": "./feature-browser.js",
"node": "./feature-node.js",
"default": "./feature.js"
}
}
}
```

Defines a package where `require('pkg/feature')` and `import 'pkg/feature'`
could provide different implementations between the browser and Node.js,
given third-party tool support for a `"browser"` condition.
could provide different implementations between Node.js and other JS
environments.

When using environment branches, always include a `"default"` condition where
possible. Providing a `"default"` condition ensures that any unknown JS
environments are able to use this universal implementation, which helps avoid
these JS environments from having to pretend to be existing environments in
order to support packages with conditional exports. For this reason, using
`"node"` and `"default"` condition branches is usually preferable to using
`"node"` and `"browser"` condition branches.

#### Nested conditions

Expand All @@ -479,11 +487,11 @@ use in Node.js but not the browser:
{
"main": "./main.js",
"exports": {
"browser": "./feature-browser.mjs",
"node": {
"import": "./feature-node.mjs",
"require": "./feature-node.cjs"
}
},
"default": "./feature.mjs",
}
}
```
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