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Update to latest implementation changes #38

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Jul 30, 2019
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Update to latest implementation changes #38

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12 changes: 3 additions & 9 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -31,14 +31,9 @@ We propose a field in `package.json` to specify one or more entrypoint locations

The `package.json` `"exports"` interface will only be respected for bare specifiers, e.g. `import _ from 'lodash'` where the specifier `'lodash'` doesn’t start with a `.` or `/`.

`"exports"` works in concert with the `package.json` `"type": "module"` signifier that a package can be imported as ESM by Node.
`"exports"` by itself does not signify that a package should be treated as ESM, but `"exports"` is currently ignored for packages `require`d as CommonJS.
Extending this feature to CommonJS may occur in the future, but issues of backward compatibility would need to be addressed.
At the moment `"exports"` is limited to ESM packages or dual ESM/CommonJS packages that are imported as ESM.
`"exports"` works in concert with the `package.json` `"type": "module"` signifier that a package can be imported as ESM by Node - `"exports"` by itself does not signify that a package should be treated as ESM.

For `"type": "module"` packages with both `"main"` and `"exports"`, a main entrypoint defined by `"exports"` takes precedence over one defined by `"main"`.
This allows a package to be importable as either ESM or CommonJS.
If a `package.json` lacks `"exports"` but includes `"type": "module"`, `"main"` defines the package’s ESM entrypoint.
This feature can be supported for both CommonJS and ES modules.

For packages that only have a main and no exports, `"exports": false` can be used as a shorthand for `"exports": {}` providing an encapsulated package.

Expand All @@ -53,15 +48,14 @@ Here’s a complete `package.json` example, for a hypothetical module named `@mo
"type": "module",
"main": "./dist/index.js",
"exports": {
".": "./src/moment.mjs",
"./": "./src/util/",
"./timezones/": "./data/timezones/",
"./timezones/utc": "./data/timezones/utc/index.mjs"
}
}
```

Within the `"exports"` object, the key string after the `'.'` is concatenated on the end of the name field, e.g. `import utc from '@momentjs/moment/timezones/utc'` is formed from `'@momentjs/moment'` + `'/timezones/utc'`. Note that this is string manipulation, not a file path: `"./timezones/utc"` is allowed, but just `"timezones/utc"` is not. The `.` is a placeholder representing the package name. The main entrypoint is therefore the dot string, `".": "./src/moment.mjs"`.
Within the `"exports"` object, the key string after the `'.'` is concatenated on the end of the name field, e.g. `import utc from '@momentjs/moment/timezones/utc'` is formed from `'@momentjs/moment'` + `'/timezones/utc'`. Note that this is string manipulation, not a file path: `"./timezones/utc"` is allowed, but just `"timezones/utc"` is not.

Keys that end in slashes can map to folder roots, following the [pattern in the browser import maps proposal](https://github.com/WICG/import-maps#packages-via-trailing-slashes): `"./timezones/": "./data/timezones/"` would allow `import pdt from "@momentjs/moment/timezones/pdt.mjs"` to import `./data/timezones/pdt.mjs`.

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