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enhanced-resolve

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 lookupStartPath = '/Users/webpack/some/root/dir';
const request = './path/to-look-up.js';
myResolver.resolve({}, lookupStartPath, request, (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
modules ["node_modules"] A list of directories to resolve modules from, can be absolute path or folder name
descriptionFiles ["package.json"] A list of description files to read from
plugins [] A list of additional resolve plugins which should be applied
mainFields ["main"] A list of main fields in description files
aliasFields [] A list of alias fields in description files
mainFiles ["index"] A list of main files in directories
extensions [".js", ".json", ".node"] A list of extensions which should be tried for files
enforceExtension false Enforce that a extension from extensions must be used
moduleExtensions [] A list of module extensions which should be tried for modules
enforceModuleExtension false Enforce that a extension from moduleExtensions must be used
alias [] A list of module alias configurations or an object which maps key to value
resolveToContext false Resolve to a context instead of a file
unsafeCache false Use this cache object to unsafely cache the successful requests
cacheWithContext true If unsafe cache is enabled, includes request.context in the cache key
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.
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) {
    resolver.plugin(this.source, (request, callback) => {
      // Any logic you need to create a new `request` can go here 
      resolver.doResolve(this.target, request, null, 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

Build Status

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

Copyright (c) 2012-2016 Tobias Koppers

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