459 lines
15 KiB
Markdown
459 lines
15 KiB
Markdown
# resolve.exports [](https://github.com/lukeed/resolve.exports/actions) [](https://codecov.io/gh/lukeed/resolve.exports)
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> A tiny (952b), correct, general-purpose, and configurable `"exports"` and `"imports"` resolver without file-system reliance
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***Why?***
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Hopefully, this module may serve as a reference point (and/or be used directly) so that the varying tools and bundlers within the ecosystem can share a common approach with one another **as well as** with the native Node.js implementation.
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With the push for ESM, we must be _very_ careful and avoid fragmentation. If we, as a community, begin propagating different _dialects_ of the resolution algorithm, then we're headed for deep trouble. It will make supporting (and using) `"exports"` nearly impossible, which may force its abandonment and along with it, its benefits.
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Let's have nice things.
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## Install
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```sh
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$ npm install resolve.exports
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```
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## Usage
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> Please see [`/test/`](/test) for examples.
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```js
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import * as resolve from 'resolve.exports';
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// package.json contents
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const pkg = {
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"name": "foobar",
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"module": "dist/module.mjs",
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"main": "dist/require.js",
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"imports": {
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"#hash": {
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"import": {
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"browser": "./hash/web.mjs",
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"node": "./hash/node.mjs",
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},
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"default": "./hash/detect.js"
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}
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},
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"exports": {
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".": {
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"import": "./dist/module.mjs",
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"require": "./dist/require.js"
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},
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"./lite": {
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"worker": {
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"browser": "./lite/worker.browser.js",
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"node": "./lite/worker.node.js"
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},
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"import": "./lite/module.mjs",
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"require": "./lite/require.js"
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}
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}
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};
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// ---
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// Exports
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// ---
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// entry: "foobar" === "." === default
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// conditions: ["default", "import", "node"]
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resolve.exports(pkg);
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resolve.exports(pkg, '.');
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resolve.exports(pkg, 'foobar');
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//=> ["./dist/module.mjs"]
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// entry: "foobar/lite" === "./lite"
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// conditions: ["default", "import", "node"]
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resolve.exports(pkg, 'foobar/lite');
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resolve.exports(pkg, './lite');
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//=> ["./lite/module.mjs"]
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// Enable `require` condition
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// conditions: ["default", "require", "node"]
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resolve.exports(pkg, 'foobar', { require: true }); //=> ["./dist/require.js"]
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resolve.exports(pkg, './lite', { require: true }); //=> ["./lite/require.js"]
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// Throws "Missing <entry> specifier in <name> package" Error
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resolve.exports(pkg, 'foobar/hello');
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resolve.exports(pkg, './hello/world');
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// Add custom condition(s)
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// conditions: ["default", "worker", "import", "node"]
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resolve.exports(pkg, 'foobar/lite', {
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conditions: ['worker']
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}); //=> ["./lite/worker.node.js"]
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// Toggle "browser" condition
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// conditions: ["default", "worker", "import", "browser"]
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resolve.exports(pkg, 'foobar/lite', {
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conditions: ['worker'],
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browser: true
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}); //=> ["./lite/worker.browser.js"]
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// Disable non-"default" condition activate
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// NOTE: breaks from Node.js default behavior
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// conditions: ["default", "custom"]
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resolve.exports(pkg, 'foobar/lite', {
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conditions: ['custom'],
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unsafe: true,
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});
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//=> Error: No known conditions for "./lite" specifier in "foobar" package
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// ---
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// Imports
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// ---
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// conditions: ["default", "import", "node"]
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resolve.imports(pkg, '#hash');
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resolve.imports(pkg, 'foobar/#hash');
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//=> ["./hash/node.mjs"]
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// conditions: ["default", "import", "browser"]
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resolve.imports(pkg, '#hash', { browser: true });
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resolve.imports(pkg, 'foobar/#hash');
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//=> ["./hash/web.mjs"]
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// conditions: ["default"]
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resolve.imports(pkg, '#hash', { unsafe: true });
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resolve.imports(pkg, 'foobar/#hash');
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//=> ["./hash/detect.mjs"]
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resolve.imports(pkg, '#hello/world');
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resolve.imports(pkg, 'foobar/#hello/world');
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//=> Error: Missing "#hello/world" specifier in "foobar" package
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// ---
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// Legacy
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// ---
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// prefer "module" > "main" (default)
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resolve.legacy(pkg); //=> "dist/module.mjs"
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// customize fields order
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resolve.legacy(pkg, {
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fields: ['main', 'module']
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}); //=> "dist/require.js"
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```
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## API
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The [`resolve()`](#resolvepkg-entry-options), [`exports()`](#exportspkg-entry-options), and [`imports()`](#importspkg-target-options) functions share similar API signatures:
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```ts
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export function resolve(pkg: Package, entry?: string, options?: Options): string[] | undefined;
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export function exports(pkg: Package, entry?: string, options?: Options): string[] | undefined;
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export function imports(pkg: Package, target: string, options?: Options): string[] | undefined;
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// ^ not optional!
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```
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All three:
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* accept a `package.json` file's contents as a JSON object
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* accept a target/entry identifier
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* may accept an [Options](#options) object
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* return `string[]`, `string`, or `undefined`
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The only difference is that `imports()` must accept a target identifier as there can be no inferred default.
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See below for further API descriptions.
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> **Note:** There is also a [Legacy Resolver API](#legacy-resolver)
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---
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### resolve(pkg, entry?, options?)
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Returns: `string[]` or `undefined`
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A convenience helper which automatically reroutes to [`exports()`](#exportspkg-entry-options) or [`imports()`](#importspkg-target-options) depending on the `entry` value.
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When unspecified, `entry` defaults to the `"."` identifier, which means that `exports()` will be invoked.
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```js
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import * as r from 'resolve.exports';
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let pkg = {
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name: 'foobar',
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// ...
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};
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r.resolve(pkg);
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//~> r.exports(pkg, '.');
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r.resolve(pkg, 'foobar');
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//~> r.exports(pkg, '.');
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r.resolve(pkg, 'foobar/subpath');
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//~> r.exports(pkg, './subpath');
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r.resolve(pkg, '#hash/md5');
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//~> r.imports(pkg, '#hash/md5');
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r.resolve(pkg, 'foobar/#hash/md5');
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//~> r.imports(pkg, '#hash/md5');
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```
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### exports(pkg, entry?, options?)
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Returns: `string[]` or `undefined`
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Traverse the `"exports"` within the contents of a `package.json` file. <br>
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If the contents _does not_ contain an `"exports"` map, then `undefined` will be returned.
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Successful resolutions will always result in a `string` or `string[]` value. This will be the value of the resolved mapping itself – which means that the output is a relative file path.
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This function may throw an Error if:
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* the requested `entry` cannot be resolved (aka, not defined in the `"exports"` map)
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* an `entry` _is_ defined but no known conditions were matched (see [`options.conditions`](#optionsconditions))
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#### pkg
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Type: `object` <br>
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Required: `true`
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The `package.json` contents.
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#### entry
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Type: `string` <br>
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Required: `false` <br>
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Default: `.` (aka, root)
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The desired target entry, or the original `import` path.
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When `entry` _is not_ a relative path (aka, does not start with `'.'`), then `entry` is given the `'./'` prefix.
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When `entry` begins with the package name (determined via the `pkg.name` value), then `entry` is truncated and made relative.
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When `entry` is already relative, it is accepted as is.
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***Examples***
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Assume we have a module named "foobar" and whose `pkg` contains `"name": "foobar"`.
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| `entry` value | treated as | reason |
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|-|-|-|
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| `null` / `undefined` | `'.'` | default |
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| `'.'` | `'.'` | value was relative |
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| `'foobar'` | `'.'` | value was `pkg.name` |
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| `'foobar/lite'` | `'./lite'` | value had `pkg.name` prefix |
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| `'./lite'` | `'./lite'` | value was relative |
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| `'lite'` | `'./lite'` | value was not relative & did not have `pkg.name` prefix |
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### imports(pkg, target, options?)
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Returns: `string[]` or `undefined`
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Traverse the `"imports"` within the contents of a `package.json` file. <br>
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If the contents _does not_ contain an `"imports"` map, then `undefined` will be returned.
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Successful resolutions will always result in a `string` or `string[]` value. This will be the value of the resolved mapping itself – which means that the output is a relative file path.
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This function may throw an Error if:
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* the requested `target` cannot be resolved (aka, not defined in the `"imports"` map)
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* an `target` _is_ defined but no known conditions were matched (see [`options.conditions`](#optionsconditions))
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#### pkg
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Type: `object` <br>
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Required: `true`
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The `package.json` contents.
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#### target
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Type: `string` <br>
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Required: `true`
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The target import identifier; for example, `#hash` or `#hash/md5`.
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Import specifiers _must_ begin with the `#` character, as required by the resolution specification. However, if `target` begins with the package name (determined by the `pkg.name` value), then `resolve.exports` will trim it from the `target` identifier. For example, `"foobar/#hash/md5"` will be treated as `"#hash/md5"` for the `"foobar"` package.
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## Options
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The [`resolve()`](#resolvepkg-entry-options), [`imports()`](#importspkg-target-options), and [`exports()`](#exportspkg-entry-options) functions share these options. All properties are optional and you are not required to pass an `options` argument.
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Collectively, the `options` are used to assemble a list of [conditions](https://nodejs.org/docs/latest-v18.x/api/packages.html#conditional-exports) that should be activated while resolving your target(s).
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> **Note:** Although the Node.js documentation primarily showcases conditions alongside `"exports"` usage, they also apply to `"imports"` maps too. _([example](https://nodejs.org/docs/latest-v18.x/api/packages.html#subpath-imports))_
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#### options.require
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Type: `boolean` <br>
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Default: `false`
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When truthy, the `"require"` field is added to the list of allowed/known conditions. <br>
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Otherwise the `"import"` field is added instead.
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#### options.browser
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Type: `boolean` <br>
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Default: `false`
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When truthy, the `"browser"` field is added to the list of allowed/known conditions. <br>
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Otherwise the `"node"` field is added instead.
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#### options.conditions
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Type: `string[]` <br>
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Default: `[]`
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A list of additional/custom conditions that should be accepted when seen.
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> **Important:** The order specified within `options.conditions` does not matter. <br>The matching order/priority is **always** determined by the `"exports"` map's key order.
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For example, you may choose to accept a `"production"` condition in certain environments. Given the following `pkg` content:
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```js
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const pkg = {
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// package.json ...
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"exports": {
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"worker": "./$worker.js",
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"require": "./$require.js",
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"production": "./$production.js",
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"import": "./$import.mjs",
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}
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};
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resolve.exports(pkg, '.');
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// Conditions: ["default", "import", "node"]
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//=> ["./$import.mjs"]
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resolve.exports(pkg, '.', {
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conditions: ['production']
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});
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// Conditions: ["default", "production", "import", "node"]
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//=> ["./$production.js"]
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resolve.exports(pkg, '.', {
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conditions: ['production'],
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require: true,
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});
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// Conditions: ["default", "production", "require", "node"]
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//=> ["./$require.js"]
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resolve.exports(pkg, '.', {
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conditions: ['production', 'worker'],
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require: true,
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});
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// Conditions: ["default", "production", "worker", "require", "node"]
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//=> ["./$worker.js"]
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resolve.exports(pkg, '.', {
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conditions: ['production', 'worker']
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});
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// Conditions: ["default", "production", "worker", "import", "node"]
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//=> ["./$worker.js"]
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```
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#### options.unsafe
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Type: `boolean` <br>
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Default: `false`
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> **Important:** You probably do not want this option! <br>It will break out of Node's default resolution conditions.
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When enabled, this option will ignore **all other options** except [`options.conditions`](#optionsconditions). This is because, when enabled, `options.unsafe` **does not** assume or provide any default conditions except the `"default"` condition.
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```js
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resolve.exports(pkg, '.');
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//=> Conditions: ["default", "import", "node"]
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resolve.exports(pkg, '.', { unsafe: true });
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//=> Conditions: ["default"]
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resolve.exports(pkg, '.', { unsafe: true, require: true, browser: true });
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//=> Conditions: ["default"]
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```
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In other words, this means that trying to use `options.require` or `options.browser` alongside `options.unsafe` will have no effect. In order to enable these conditions, you must provide them manually into the `options.conditions` list:
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```js
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resolve.exports(pkg, '.', {
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unsafe: true,
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conditions: ["require"]
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});
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//=> Conditions: ["default", "require"]
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resolve.exports(pkg, '.', {
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unsafe: true,
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conditions: ["browser", "require", "custom123"]
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});
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//=> Conditions: ["default", "browser", "require", "custom123"]
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```
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## Legacy Resolver
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Also included is a "legacy" method for resolving non-`"exports"` package fields. This may be used as a fallback method when for when no `"exports"` mapping is defined. In other words, it's completely optional (and tree-shakeable).
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### legacy(pkg, options?)
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Returns: `string` or `undefined`
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You may customize the field priority via [`options.fields`](#optionsfields).
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When a field is found, its value is returned _as written_. <br>
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When no fields were found, `undefined` is returned. If you wish to mimic Node.js behavior, you can assume this means `'index.js'` – but this module does not make that assumption for you.
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#### options.browser
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Type: `boolean` or `string` <br>
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Default: `false`
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When truthy, ensures that the `'browser'` field is part of the acceptable `fields` list.
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> **Important:** If your custom [`options.fields`](#optionsfields) value includes `'browser'`, then _your_ order is respected. <br>Otherwise, when truthy, `options.browser` will move `'browser'` to the front of the list, making it the top priority.
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When `true` and `"browser"` is an object, then `legacy()` will return the the entire `"browser"` object.
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You may also pass a string value, which will be treated as an import/file path. When this is the case and `"browser"` is an object, then `legacy()` may return:
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* `false` – if the package author decided a file should be ignored; or
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* your `options.browser` string value – but made relative, if not already
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> See the [`"browser" field specification](https://github.com/defunctzombie/package-browser-field-spec) for more information.
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#### options.fields
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Type: `string[]` <br>
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Default: `['module', 'main']`
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A list of fields to accept. The order of the array determines the priority/importance of each field, with the most important fields at the beginning of the list.
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By default, the `legacy()` method will accept any `"module"` and/or "main" fields if they are defined. However, if both fields are defined, then "module" will be returned.
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```js
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import { legacy } from 'resolve.exports';
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// package.json
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const pkg = {
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"name": "...",
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"worker": "worker.js",
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"module": "module.mjs",
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"browser": "browser.js",
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"main": "main.js",
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};
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legacy(pkg);
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// fields = [module, main]
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//=> "module.mjs"
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legacy(pkg, { browser: true });
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// fields = [browser, module, main]
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//=> "browser.mjs"
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legacy(pkg, {
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fields: ['missing', 'worker', 'module', 'main']
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});
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// fields = [missing, worker, module, main]
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//=> "worker.js"
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legacy(pkg, {
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fields: ['missing', 'worker', 'module', 'main'],
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browser: true,
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});
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// fields = [browser, missing, worker, module, main]
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//=> "browser.js"
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legacy(pkg, {
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fields: ['module', 'browser', 'main'],
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browser: true,
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});
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// fields = [module, browser, main]
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//=> "module.mjs"
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```
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## License
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MIT © [Luke Edwards](https://lukeed.com)
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