1# resolve <sup>[![Version Badge][2]][1]</sup>
2
3implements the [node `require.resolve()` algorithm](https://nodejs.org/api/modules.html#modules_all_together) such that you can `require.resolve()` on behalf of a file asynchronously and synchronously
4
5[![github actions][actions-image]][actions-url]
6[![coverage][codecov-image]][codecov-url]
7[![dependency status][5]][6]
8[![dev dependency status][7]][8]
9[![License][license-image]][license-url]
10[![Downloads][downloads-image]][downloads-url]
11
12[![npm badge][11]][1]
13
14# example
15
16asynchronously resolve:
17
18```js
19var resolve = require('resolve/async'); // or, require('resolve')
20resolve('tap', { basedir: __dirname }, function (err, res) {
21    if (err) console.error(err);
22    else console.log(res);
23});
24```
25
26```
27$ node example/async.js
28/home/substack/projects/node-resolve/node_modules/tap/lib/main.js
29```
30
31synchronously resolve:
32
33```js
34var resolve = require('resolve/sync'); // or, `require('resolve').sync
35var res = resolve('tap', { basedir: __dirname });
36console.log(res);
37```
38
39```
40$ node example/sync.js
41/home/substack/projects/node-resolve/node_modules/tap/lib/main.js
42```
43
44# methods
45
46```js
47var resolve = require('resolve');
48var async = require('resolve/async');
49var sync = require('resolve/sync');
50```
51
52For both the synchronous and asynchronous methods, errors may have any of the following `err.code` values:
53
54- `MODULE_NOT_FOUND`: the given path string (`id`) could not be resolved to a module
55- `INVALID_BASEDIR`: the specified `opts.basedir` doesn't exist, or is not a directory
56- `INVALID_PACKAGE_MAIN`: a `package.json` was encountered with an invalid `main` property (eg. not a string)
57
58## resolve(id, opts={}, cb)
59
60Asynchronously resolve the module path string `id` into `cb(err, res [, pkg])`, where `pkg` (if defined) is the data from `package.json`.
61
62options are:
63
64* opts.basedir - directory to begin resolving from
65
66* opts.package - `package.json` data applicable to the module being loaded
67
68* opts.extensions - array of file extensions to search in order
69
70* opts.includeCoreModules - set to `false` to exclude node core modules (e.g. `fs`) from the search
71
72* opts.readFile - how to read files asynchronously
73
74* opts.isFile - function to asynchronously test whether a file exists
75
76* opts.isDirectory - function to asynchronously test whether a file exists and is a directory
77
78* opts.realpath - function to asynchronously resolve a potential symlink to its real path
79
80* `opts.readPackage(readFile, pkgfile, cb)` - function to asynchronously read and parse a package.json file
81  * readFile - the passed `opts.readFile` or `fs.readFile` if not specified
82  * pkgfile - path to package.json
83  * cb - callback
84
85* `opts.packageFilter(pkg, pkgfile, dir)` - transform the parsed package.json contents before looking at the "main" field
86  * pkg - package data
87  * pkgfile - path to package.json
88  * dir - directory that contains package.json
89
90* `opts.pathFilter(pkg, path, relativePath)` - transform a path within a package
91  * pkg - package data
92  * path - the path being resolved
93  * relativePath - the path relative from the package.json location
94  * returns - a relative path that will be joined from the package.json location
95
96* opts.paths - require.paths array to use if nothing is found on the normal `node_modules` recursive walk (probably don't use this)
97
98  For advanced users, `paths` can also be a `opts.paths(request, start, opts)` function
99    * request - the import specifier being resolved
100    * start - lookup path
101    * getNodeModulesDirs - a thunk (no-argument function) that returns the paths using standard `node_modules` resolution
102    * opts - the resolution options
103
104* `opts.packageIterator(request, start, opts)` - return the list of candidate paths where the packages sources may be found (probably don't use this)
105    * request - the import specifier being resolved
106    * start - lookup path
107    * getPackageCandidates - a thunk (no-argument function) that returns the paths using standard `node_modules` resolution
108    * opts - the resolution options
109
110* opts.moduleDirectory - directory (or directories) in which to recursively look for modules. default: `"node_modules"`
111
112* opts.preserveSymlinks - if true, doesn't resolve `basedir` to real path before resolving.
113This is the way Node resolves dependencies when executed with the [--preserve-symlinks](https://nodejs.org/api/all.html#cli_preserve_symlinks) flag.
114**Note:** this property is currently `true` by default but it will be changed to
115`false` in the next major version because *Node's resolution algorithm does not preserve symlinks by default*.
116
117default `opts` values:
118
119```js
120{
121    paths: [],
122    basedir: __dirname,
123    extensions: ['.js'],
124    includeCoreModules: true,
125    readFile: fs.readFile,
126    isFile: function isFile(file, cb) {
127        fs.stat(file, function (err, stat) {
128            if (!err) {
129                return cb(null, stat.isFile() || stat.isFIFO());
130            }
131            if (err.code === 'ENOENT' || err.code === 'ENOTDIR') return cb(null, false);
132            return cb(err);
133        });
134    },
135    isDirectory: function isDirectory(dir, cb) {
136        fs.stat(dir, function (err, stat) {
137            if (!err) {
138                return cb(null, stat.isDirectory());
139            }
140            if (err.code === 'ENOENT' || err.code === 'ENOTDIR') return cb(null, false);
141            return cb(err);
142        });
143    },
144    realpath: function realpath(file, cb) {
145        var realpath = typeof fs.realpath.native === 'function' ? fs.realpath.native : fs.realpath;
146        realpath(file, function (realPathErr, realPath) {
147            if (realPathErr && realPathErr.code !== 'ENOENT') cb(realPathErr);
148            else cb(null, realPathErr ? file : realPath);
149        });
150    },
151    readPackage: function defaultReadPackage(readFile, pkgfile, cb) {
152        readFile(pkgfile, function (readFileErr, body) {
153            if (readFileErr) cb(readFileErr);
154            else {
155                try {
156                    var pkg = JSON.parse(body);
157                    cb(null, pkg);
158                } catch (jsonErr) {
159                    cb(null);
160                }
161            }
162        });
163    },
164    moduleDirectory: 'node_modules',
165    preserveSymlinks: true
166}
167```
168
169## resolve.sync(id, opts)
170
171Synchronously resolve the module path string `id`, returning the result and
172throwing an error when `id` can't be resolved.
173
174options are:
175
176* opts.basedir - directory to begin resolving from
177
178* opts.extensions - array of file extensions to search in order
179
180* opts.includeCoreModules - set to `false` to exclude node core modules (e.g. `fs`) from the search
181
182* opts.readFileSync - how to read files synchronously
183
184* opts.isFile - function to synchronously test whether a file exists
185
186* opts.isDirectory - function to synchronously test whether a file exists and is a directory
187
188* opts.realpathSync - function to synchronously resolve a potential symlink to its real path
189
190* `opts.readPackageSync(readFileSync, pkgfile)` - function to synchronously read and parse a package.json file
191  * readFileSync - the passed `opts.readFileSync` or `fs.readFileSync` if not specified
192  * pkgfile - path to package.json
193
194* `opts.packageFilter(pkg, dir)` - transform the parsed package.json contents before looking at the "main" field
195  * pkg - package data
196  * dir - directory that contains package.json (Note: the second argument will change to "pkgfile" in v2)
197
198* `opts.pathFilter(pkg, path, relativePath)` - transform a path within a package
199  * pkg - package data
200  * path - the path being resolved
201  * relativePath - the path relative from the package.json location
202  * returns - a relative path that will be joined from the package.json location
203
204* opts.paths - require.paths array to use if nothing is found on the normal `node_modules` recursive walk (probably don't use this)
205
206  For advanced users, `paths` can also be a `opts.paths(request, start, opts)` function
207    * request - the import specifier being resolved
208    * start - lookup path
209    * getNodeModulesDirs - a thunk (no-argument function) that returns the paths using standard `node_modules` resolution
210    * opts - the resolution options
211
212* `opts.packageIterator(request, start, opts)` - return the list of candidate paths where the packages sources may be found (probably don't use this)
213    * request - the import specifier being resolved
214    * start - lookup path
215    * getPackageCandidates - a thunk (no-argument function) that returns the paths using standard `node_modules` resolution
216    * opts - the resolution options
217
218* opts.moduleDirectory - directory (or directories) in which to recursively look for modules. default: `"node_modules"`
219
220* opts.preserveSymlinks - if true, doesn't resolve `basedir` to real path before resolving.
221This is the way Node resolves dependencies when executed with the [--preserve-symlinks](https://nodejs.org/api/all.html#cli_preserve_symlinks) flag.
222**Note:** this property is currently `true` by default but it will be changed to
223`false` in the next major version because *Node's resolution algorithm does not preserve symlinks by default*.
224
225default `opts` values:
226
227```js
228{
229    paths: [],
230    basedir: __dirname,
231    extensions: ['.js'],
232    includeCoreModules: true,
233    readFileSync: fs.readFileSync,
234    isFile: function isFile(file) {
235        try {
236            var stat = fs.statSync(file);
237        } catch (e) {
238            if (e && (e.code === 'ENOENT' || e.code === 'ENOTDIR')) return false;
239            throw e;
240        }
241        return stat.isFile() || stat.isFIFO();
242    },
243    isDirectory: function isDirectory(dir) {
244        try {
245            var stat = fs.statSync(dir);
246        } catch (e) {
247            if (e && (e.code === 'ENOENT' || e.code === 'ENOTDIR')) return false;
248            throw e;
249        }
250        return stat.isDirectory();
251    },
252    realpathSync: function realpathSync(file) {
253        try {
254            var realpath = typeof fs.realpathSync.native === 'function' ? fs.realpathSync.native : fs.realpathSync;
255            return realpath(file);
256        } catch (realPathErr) {
257            if (realPathErr.code !== 'ENOENT') {
258                throw realPathErr;
259            }
260        }
261        return file;
262    },
263    readPackageSync: function defaultReadPackageSync(readFileSync, pkgfile) {
264        var body = readFileSync(pkgfile);
265        try {
266            var pkg = JSON.parse(body);
267            return pkg;
268        } catch (jsonErr) {}
269    },
270    moduleDirectory: 'node_modules',
271    preserveSymlinks: true
272}
273```
274
275# install
276
277With [npm](https://npmjs.org) do:
278
279```sh
280npm install resolve
281```
282
283# license
284
285MIT
286
287[1]: https://npmjs.org/package/resolve
288[2]: https://versionbadg.es/browserify/resolve.svg
289[5]: https://david-dm.org/browserify/resolve.svg
290[6]: https://david-dm.org/browserify/resolve
291[7]: https://david-dm.org/browserify/resolve/dev-status.svg
292[8]: https://david-dm.org/browserify/resolve#info=devDependencies
293[11]: https://nodei.co/npm/resolve.png?downloads=true&stars=true
294[license-image]: https://img.shields.io/npm/l/resolve.svg
295[license-url]: LICENSE
296[downloads-image]: https://img.shields.io/npm/dm/resolve.svg
297[downloads-url]: https://npm-stat.com/charts.html?package=resolve
298[codecov-image]: https://codecov.io/gh/browserify/resolve/branch/main/graphs/badge.svg
299[codecov-url]: https://app.codecov.io/gh/browserify/resolve/
300[actions-image]: https://img.shields.io/endpoint?url=https://github-actions-badge-u3jn4tfpocch.runkit.sh/browserify/resolve
301[actions-url]: https://github.com/browserify/resolve/actions
302