# enhanced-resolve
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[![Build Status][build-status]][build-status-url]
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Offers an async require.resolve function. It's highly configurable.
## Features
- plugin system
- provide a custom filesystem
- sync and async node.js filesystems included
## Getting Started
### Install
```sh
# npm
npm install enhanced-resolve
# or Yarn
yarn add enhanced-resolve
```
### Resolve
There is a Node.js API which allows to resolve requests according to the Node.js resolving rules.
Sync and async APIs are offered. A `create` method allows to create a custom resolve function.
```js
const resolve = require("enhanced-resolve");
resolve("/some/path/to/folder", "module/dir", (err, result) => {
result; // === "/some/path/node_modules/module/dir/index.js"
});
resolve.sync("/some/path/to/folder", "../../dir");
// === "/some/path/dir/index.js"
const myResolve = resolve.create({
// or resolve.create.sync
extensions: [".ts", ".js"]
// see more options below
});
myResolve("/some/path/to/folder", "ts-module", (err, result) => {
result; // === "/some/node_modules/ts-module/index.ts"
});
```
### Creating a Resolver
The easiest way to create a resolver is to use the `createResolver` function on `ResolveFactory`, along with one of the supplied File System implementations.
```js
const fs = require("fs");
const { CachedInputFileSystem, ResolverFactory } = require("enhanced-resolve");
// create a resolver
const myResolver = ResolverFactory.createResolver({
// Typical usage will consume the `fs` + `CachedInputFileSystem`, which wraps Node.js `fs` to add caching.
fileSystem: new CachedInputFileSystem(fs, 4000),
extensions: [".js", ".json"]
/* any other resolver options here. Options/defaults can be seen below */
});
// resolve a file with the new resolver
const context = {};
const lookupStartPath = "/Users/webpack/some/root/dir";
const request = "./path/to-look-up.js";
const resolveContext = {};
myResolver.resolve(context, lookupStartPath, request, resolveContext, (
err /*Error*/,
filepath /*string*/
) => {
// Do something with the path
});
```
#### Resolver Options
| Field | Default | Description |
|------------------|-----------------------------| --------------------------------------------------------------------------------------------------------------------------------------------------------- |
| alias | [] | A list of module alias configurations or an object which maps key to value |
| aliasFields | [] | A list of alias fields in description files |
| extensionAlias | {} | An object which maps extension to extension aliases |
| cachePredicate | function() { return true }; | A function which decides whether a request should be cached or not. An object is passed to the function with `path` and `request` properties. |
| cacheWithContext | true | If unsafe cache is enabled, includes `request.context` in the cache key |
| conditionNames | [] | A list of exports field condition names |
| descriptionFiles | ["package.json"] | A list of description files to read from |
| enforceExtension | false | Enforce that a extension from extensions must be used |
| exportsFields | ["exports"] | A list of exports fields in description files |
| extensions | [".js", ".json", ".node"] | A list of extensions which should be tried for files |
| fallback | [] | Same as `alias`, but only used if default resolving fails |
| fileSystem | | The file system which should be used |
| fullySpecified | false | Request passed to resolve is already fully specified and extensions or main files are not resolved for it (they are still resolved for internal requests) |
| mainFields | ["main"] | A list of main fields in description files |
| mainFiles | ["index"] | A list of main files in directories |
| modules | ["node_modules"] | A list of directories to resolve modules from, can be absolute path or folder name |
| plugins | [] | A list of additional resolve plugins which should be applied |
| resolver | undefined | A prepared Resolver to which the plugins are attached |
| resolveToContext | false | Resolve to a context instead of a file |
| preferRelative | false | Prefer to resolve module requests as relative request and fallback to resolving as module |
| preferAbsolute | false | Prefer to resolve server-relative urls as absolute paths before falling back to resolve in roots |
| restrictions | [] | A list of resolve restrictions |
| roots | [] | A list of root paths |
| symlinks | true | Whether to resolve symlinks to their symlinked location |
| unsafeCache | false | Use this cache object to unsafely cache the successful requests |
## Plugins
Similar to `webpack`, the core of `enhanced-resolve` functionality is implemented as individual plugins that are executed using [`tapable`](https://github.com/webpack/tapable).
These plugins can extend the functionality of the library, adding other ways for files/contexts to be resolved.
A plugin should be a `class` (or its ES5 equivalent) with an `apply` method. The `apply` method will receive a `resolver` instance, that can be used to hook in to the event system.
### Plugin Boilerplate
```js
class MyResolverPlugin {
constructor(source, target) {
this.source = source;
this.target = target;
}
apply(resolver) {
const target = resolver.ensureHook(this.target);
resolver
.getHook(this.source)
.tapAsync("MyResolverPlugin", (request, resolveContext, callback) => {
// Any logic you need to create a new `request` can go here
resolver.doResolve(target, request, null, resolveContext, callback);
});
}
}
```
Plugins are executed in a pipeline, and register which event they should be executed before/after. In the example above, `source` is the name of the event that starts the pipeline, and `target` is what event this plugin should fire, which is what continues the execution of the pipeline. For an example of how these different plugin events create a chain, see `lib/ResolverFactory.js`, in the `//// pipeline ////` section.
## Escaping
It's allowed to escape `#` as `\0#` to avoid parsing it as fragment.
enhanced-resolve will try to resolve requests containing `#` as path and as fragment, so it will automatically figure out if `./some#thing` means `.../some.js#thing` or `.../some#thing.js`. When a `#` is resolved as path it will be escaped in the result. Here: `.../some\0#thing.js`.
## Tests
```javascript
yarn test
```
## Passing options from webpack
If you are using `webpack`, and you want to pass custom options to `enhanced-resolve`, the options are passed from the `resolve` key of your webpack configuration e.g.:
```
resolve: {
extensions: ['.js', '.jsx'],
modules: [path.resolve(__dirname, 'src'), 'node_modules'],
plugins: [new DirectoryNamedWebpackPlugin()]
...
},
```
## License
Copyright (c) 2012-2019 JS Foundation and other contributors
MIT (http://www.opensource.org/licenses/mit-license.php)
[npm]: https://img.shields.io/npm/v/enhanced-resolve.svg
[npm-url]: https://www.npmjs.com/package/enhanced-resolve
[build-status]: https://github.com/webpack/enhanced-resolve/actions/workflows/test.yml/badge.svg?branch=master
[build-status-url]: https://github.com/webpack/enhanced-resolve/actions
[codecov-badge]: https://codecov.io/gh/webpack/enhanced-resolve/branch/main/graph/badge.svg?token=6B6NxtsZc3
[codecov-url]: https://codecov.io/gh/webpack/enhanced-resolve
[size]: https://packagephobia.com/badge?p=enhanced-resolve
[size-url]: https://packagephobia.com/result?p=enhanced-resolve
[discussion]: https://img.shields.io/github/discussions/webpack/webpack
[discussion-url]: https://github.com/webpack/webpack/discussions
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