3 implements the [node `require.resolve()`
4 algorithm](https://nodejs.org/api/modules.html#modules_all_together)
5 such that you can `require.resolve()` on behalf of a file asynchronously and
8 [![build status](https://secure.travis-ci.org/browserify/resolve.png)](http://travis-ci.org/browserify/resolve)
12 asynchronously resolve:
15 var resolve = require('resolve');
16 resolve('tap', { basedir: __dirname }, function (err, res) {
17 if (err) console.error(err);
18 else console.log(res);
23 $ node example/async.js
24 /home/substack/projects/node-resolve/node_modules/tap/lib/main.js
27 synchronously resolve:
30 var resolve = require('resolve');
31 var res = resolve.sync('tap', { basedir: __dirname });
36 $ node example/sync.js
37 /home/substack/projects/node-resolve/node_modules/tap/lib/main.js
43 var resolve = require('resolve');
46 For both the synchronous and asynchronous methods, errors may have any of the following `err.code` values:
48 - `MODULE_NOT_FOUND`: the given path string (`id`) could not be resolved to a module
49 - `INVALID_BASEDIR`: the specified `opts.basedir` doesn't exist, or is not a directory
50 - `INVALID_PACKAGE_MAIN`: a `package.json` was encountered with an invalid `main` property (eg. not a string)
52 ## resolve(id, opts={}, cb)
54 Asynchronously resolve the module path string `id` into `cb(err, res [, pkg])`, where `pkg` (if defined) is the data from `package.json`.
58 * opts.basedir - directory to begin resolving from
60 * opts.package - `package.json` data applicable to the module being loaded
62 * opts.extensions - array of file extensions to search in order
64 * opts.includeCoreModules - set to `false` to exclude node core modules (e.g. `fs`) from the search
66 * opts.readFile - how to read files asynchronously
68 * opts.isFile - function to asynchronously test whether a file exists
70 * opts.isDirectory - function to asynchronously test whether a directory exists
72 * opts.realpath - function to asynchronously resolve a potential symlink to its real path
74 * `opts.readPackage(readFile, pkgfile, cb)` - function to asynchronously read and parse a package.json file
75 * readFile - the passed `opts.readFile` or `fs.readFile` if not specified
76 * pkgfile - path to package.json
79 * `opts.packageFilter(pkg, pkgfile, dir)` - transform the parsed package.json contents before looking at the "main" field
81 * pkgfile - path to package.json
82 * dir - directory for package.json
84 * `opts.pathFilter(pkg, path, relativePath)` - transform a path within a package
86 * path - the path being resolved
87 * relativePath - the path relative from the package.json location
88 * returns - a relative path that will be joined from the package.json location
90 * opts.paths - require.paths array to use if nothing is found on the normal `node_modules` recursive walk (probably don't use this)
92 For advanced users, `paths` can also be a `opts.paths(request, start, opts)` function
93 * request - the import specifier being resolved
95 * getNodeModulesDirs - a thunk (no-argument function) that returns the paths using standard `node_modules` resolution
96 * opts - the resolution options
98 * `opts.packageIterator(request, start, opts)` - return the list of candidate paths where the packages sources may be found (probably don't use this)
99 * request - the import specifier being resolved
100 * start - lookup path
101 * getPackageCandidates - a thunk (no-argument function) that returns the paths using standard `node_modules` resolution
102 * opts - the resolution options
104 * opts.moduleDirectory - directory (or directories) in which to recursively look for modules. default: `"node_modules"`
106 * opts.preserveSymlinks - if true, doesn't resolve `basedir` to real path before resolving.
107 This is the way Node resolves dependencies when executed with the [--preserve-symlinks](https://nodejs.org/api/all.html#cli_preserve_symlinks) flag.
108 **Note:** this property is currently `true` by default but it will be changed to
109 `false` in the next major version because *Node's resolution algorithm does not preserve symlinks by default*.
111 default `opts` values:
118 includeCoreModules: true,
119 readFile: fs.readFile,
120 isFile: function isFile(file, cb) {
121 fs.stat(file, function (err, stat) {
123 return cb(null, stat.isFile() || stat.isFIFO());
125 if (err.code === 'ENOENT' || err.code === 'ENOTDIR') return cb(null, false);
129 isDirectory: function isDirectory(dir, cb) {
130 fs.stat(dir, function (err, stat) {
132 return cb(null, stat.isDirectory());
134 if (err.code === 'ENOENT' || err.code === 'ENOTDIR') return cb(null, false);
138 realpath: function realpath(file, cb) {
139 var realpath = typeof fs.realpath.native === 'function' ? fs.realpath.native : fs.realpath;
140 realpath(file, function (realPathErr, realPath) {
141 if (realPathErr && realPathErr.code !== 'ENOENT') cb(realPathErr);
142 else cb(null, realPathErr ? file : realPath);
145 readPackage: function defaultReadPackage(readFile, pkgfile, cb) {
146 readFile(pkgfile, function (readFileErr, body) {
147 if (readFileErr) cb(readFileErr);
150 var pkg = JSON.parse(body);
158 moduleDirectory: 'node_modules',
159 preserveSymlinks: true
163 ## resolve.sync(id, opts)
165 Synchronously resolve the module path string `id`, returning the result and
166 throwing an error when `id` can't be resolved.
170 * opts.basedir - directory to begin resolving from
172 * opts.extensions - array of file extensions to search in order
174 * opts.includeCoreModules - set to `false` to exclude node core modules (e.g. `fs`) from the search
176 * opts.readFileSync - how to read files synchronously
178 * opts.isFile - function to synchronously test whether a file exists
180 * opts.isDirectory - function to synchronously test whether a directory exists
182 * opts.realpathSync - function to synchronously resolve a potential symlink to its real path
184 * `opts.readPackageSync(readFileSync, pkgfile)` - function to synchronously read and parse a package.json file
185 * readFileSync - the passed `opts.readFileSync` or `fs.readFileSync` if not specified
186 * pkgfile - path to package.json
188 * `opts.packageFilter(pkg, dir)` - transform the parsed package.json contents before looking at the "main" field
190 * dir - directory for package.json (Note: the second argument will change to "pkgfile" in v2)
192 * `opts.pathFilter(pkg, path, relativePath)` - transform a path within a package
194 * path - the path being resolved
195 * relativePath - the path relative from the package.json location
196 * returns - a relative path that will be joined from the package.json location
198 * opts.paths - require.paths array to use if nothing is found on the normal `node_modules` recursive walk (probably don't use this)
200 For advanced users, `paths` can also be a `opts.paths(request, start, opts)` function
201 * request - the import specifier being resolved
202 * start - lookup path
203 * getNodeModulesDirs - a thunk (no-argument function) that returns the paths using standard `node_modules` resolution
204 * opts - the resolution options
206 * `opts.packageIterator(request, start, opts)` - return the list of candidate paths where the packages sources may be found (probably don't use this)
207 * request - the import specifier being resolved
208 * start - lookup path
209 * getPackageCandidates - a thunk (no-argument function) that returns the paths using standard `node_modules` resolution
210 * opts - the resolution options
212 * opts.moduleDirectory - directory (or directories) in which to recursively look for modules. default: `"node_modules"`
214 * opts.preserveSymlinks - if true, doesn't resolve `basedir` to real path before resolving.
215 This is the way Node resolves dependencies when executed with the [--preserve-symlinks](https://nodejs.org/api/all.html#cli_preserve_symlinks) flag.
216 **Note:** this property is currently `true` by default but it will be changed to
217 `false` in the next major version because *Node's resolution algorithm does not preserve symlinks by default*.
219 default `opts` values:
226 includeCoreModules: true,
227 readFileSync: fs.readFileSync,
228 isFile: function isFile(file) {
230 var stat = fs.statSync(file);
232 if (e && (e.code === 'ENOENT' || e.code === 'ENOTDIR')) return false;
235 return stat.isFile() || stat.isFIFO();
237 isDirectory: function isDirectory(dir) {
239 var stat = fs.statSync(dir);
241 if (e && (e.code === 'ENOENT' || e.code === 'ENOTDIR')) return false;
244 return stat.isDirectory();
246 realpathSync: function realpathSync(file) {
248 var realpath = typeof fs.realpathSync.native === 'function' ? fs.realpathSync.native : fs.realpathSync;
249 return realpath(file);
250 } catch (realPathErr) {
251 if (realPathErr.code !== 'ENOENT') {
257 readPackageSync: function defaultReadPackageSync(readFileSync, pkgfile) {
258 var body = readFileSync(pkgfile);
260 var pkg = JSON.parse(body);
264 moduleDirectory: 'node_modules',
265 preserveSymlinks: true
271 With [npm](https://npmjs.org) do: