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

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 {
  NodeJsInputFileSystem,
  CachedInputFileSystem,
  ResolverFactory
} = require('enhanced-resolve');

// create a resolver
const myResolver = ResolverFactory.createResolver({
  // Typical usage will consume the `NodeJsInputFileSystem` + `CachedInputFileSystem`, which wraps the Node.js `fs` wrapper to add resilience + caching.
  fileSystem: new CachedInputFileSystem(new NodeJsInputFileSystem(), 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 resolveContext = {};
const lookupStartPath = '/Users/webpack/some/root/dir';
const request = './path/to-look-up.js';
myResolver.resolve({}, lookupStartPath, request, resolveContext, (err/*Error*/, filepath/*string*/) => {
  // Do something with the path
});

For more examples creating different types resolvers (sync/async, context, etc) see lib/node.js.

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
cacheWithContext	true	If unsafe cache is enabled, includes `request.context` in the cache key
descriptionFiles	[“package.json”]	A list of description files to read from
enforceExtension	false	Enforce that a extension from extensions must be used
enforceModuleExtension	false	Enforce that a extension from moduleExtensions must be used
extensions	[“.js”, “.json”, “.node”]	A list of extensions which should be tried for files
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
roots	[]	A list of directories to resolve request starting with `/` from
ignoreRootsErrors	false	Ignore fatal errors happening during handling of `roots` (allows to add `roots` without a breaking change)
preferAbsolute	false	Prefer to resolve server-relative urls as absolute paths before falling back to resolve in roots
unsafeCache	false	Use this cache object to unsafely cache the successful requests
plugins	[]	A list of additional resolve plugins which should be applied
symlinks	true	Whether to resolve symlinks to their symlinked location
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.
moduleExtensions	[]	A list of module extensions which should be tried for modules
resolveToContext	false	Resolve to a context instead of a file
restrictions	[]	A list of resolve restrictions
fileSystem		The file system which should be used
resolver	undefined	A prepared Resolver to which the plugins are attached

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.

Tests

npm 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: ['src', 'node_modules'],
  plugins: [new DirectoryNamedWebpackPlugin()]
  ...
},

License

MIT (http://www.opensource.org/licenses/mit-license.php)