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

1# npm
2npm install enhanced-resolve
3# or Yarn
4yarn 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.

1const resolve = require("enhanced-resolve");
2
3resolve("/some/path/to/folder", "module/dir", (err, result) => {
4	result; // === "/some/path/node_modules/module/dir/index.js"
5});
6
7resolve.sync("/some/path/to/folder", "../../dir");
8// === "/some/path/dir/index.js"
9
10const myResolve = resolve.create({
11	// or resolve.create.sync
12	extensions: [".ts", ".js"],
13	// see more options below
14});
15
16myResolve("/some/path/to/folder", "ts-module", (err, result) => {
17	result; // === "/some/node_modules/ts-module/index.ts"
18});

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.

1const fs = require("fs");
2const { CachedInputFileSystem, ResolverFactory } = require("enhanced-resolve");
3
4// create a resolver
5const myResolver = ResolverFactory.createResolver({
6	// Typical usage will consume the `fs` + `CachedInputFileSystem`, which wraps Node.js `fs` to add caching.
7	fileSystem: new CachedInputFileSystem(fs, 4000),
8	extensions: [".js", ".json"],
9	/* any other resolver options here. Options/defaults can be seen below */
10});
11
12// resolve a file with the new resolver
13const context = {};
14const lookupStartPath = "/Users/webpack/some/root/dir";
15const request = "./path/to-look-up.js";
16const resolveContext = {};
17myResolver.resolve(
18	context,
19	lookupStartPath,
20	request,
21	resolveContext,
22	(err /* Error */, filepath /* string */) => {
23		// Do something with the path
24	},
25);

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

1class MyResolverPlugin {
2	constructor(source, target) {
3		this.source = source;
4		this.target = target;
5	}
6
7	apply(resolver) {
8		const target = resolver.ensureHook(this.target);
9		resolver
10			.getHook(this.source)
11			.tapAsync("MyResolverPlugin", (request, resolveContext, callback) => {
12				// Any logic you need to create a new `request` can go here
13				resolver.doResolve(target, request, null, resolveContext, callback);
14			});
15	}
16}

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

1yarn 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)