enhanced-resolve

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

# 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.

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.

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. 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

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

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)