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resolve

implements the node require.resolve() algorithm such that you can require.resolve() on behalf of a file asynchronously and synchronously

example

asynchronously resolve:

var resolve = require('resolve/async'); // or, require('resolve')
resolve('tap', { basedir: __dirname }, function (err, res) {
    if (err) console.error(err);
    else console.log(res);
});

$ node example/async.js
/home/substack/projects/node-resolve/node_modules/tap/lib/main.js

synchronously resolve:

var resolve = require('resolve/sync'); // or, `require('resolve').sync
var res = resolve('tap', { basedir: __dirname });
console.log(res);

$ node example/sync.js
/home/substack/projects/node-resolve/node_modules/tap/lib/main.js

methods

var resolve = require('resolve');
var async = require('resolve/async');
var sync = require('resolve/sync');

For both the synchronous and asynchronous methods, errors may have any of the following err.code values:

MODULE_NOT_FOUND: the given path string (id) could not be resolved to a module
INVALID_BASEDIR: the specified opts.basedir doesn't exist, or is not a directory
INVALID_PACKAGE_MAIN: a package.json was encountered with an invalid main property (eg. not a string)

resolve(id, opts={}, cb)

Asynchronously resolve the module path string id into cb(err, res [, pkg]), where pkg (if defined) is the data from package.json.

options are:

opts.basedir - directory to begin resolving from
opts.package - package.json data applicable to the module being loaded
opts.extensions - array of file extensions to search in order
opts.includeCoreModules - set to false to exclude node core modules (e.g. fs) from the search
opts.readFile - how to read files asynchronously
opts.isFile - function to asynchronously test whether a file exists
opts.isDirectory - function to asynchronously test whether a file exists and is a directory
opts.realpath - function to asynchronously resolve a potential symlink to its real path
opts.readPackage(readFile, pkgfile, cb) - function to asynchronously read and parse a package.json file
- readFile - the passed opts.readFile or fs.readFile if not specified
- pkgfile - path to package.json
- cb - callback
opts.packageFilter(pkg, pkgfile, dir) - transform the parsed package.json contents before looking at the "main" field
- pkg - package data
- pkgfile - path to package.json
- dir - directory that contains package.json
opts.pathFilter(pkg, path, relativePath) - transform a path within a package
- pkg - package data
- path - the path being resolved
- relativePath - the path relative from the package.json location
- returns - a relative path that will be joined from the package.json location
opts.paths - require.paths array to use if nothing is found on the normal node_modules recursive walk (probably don't use this)

For advanced users, paths can also be a opts.paths(request, start, opts) function
- request - the import specifier being resolved
- start - lookup path
- getNodeModulesDirs - a thunk (no-argument function) that returns the paths using standard node_modules resolution
- opts - the resolution options
opts.packageIterator(request, start, opts) - return the list of candidate paths where the packages sources may be found (probably don't use this)
- request - the import specifier being resolved
- start - lookup path
- getPackageCandidates - a thunk (no-argument function) that returns the paths using standard node_modules resolution
- opts - the resolution options
opts.moduleDirectory - directory (or directories) in which to recursively look for modules. default: "node_modules"
opts.preserveSymlinks - if true, doesn't resolve basedir to real path before resolving. This is the way Node resolves dependencies when executed with the --preserve-symlinks flag. Note: this property is currently true by default but it will be changed to false in the next major version because Node's resolution algorithm does not preserve symlinks by default.

default opts values:

{
    paths: [],
    basedir: __dirname,
    extensions: ['.js'],
    includeCoreModules: true,
    readFile: fs.readFile,
    isFile: function isFile(file, cb) {
        fs.stat(file, function (err, stat) {
            if (!err) {
                return cb(null, stat.isFile() || stat.isFIFO());
            }
            if (err.code === 'ENOENT' || err.code === 'ENOTDIR') return cb(null, false);
            return cb(err);
        });
    },
    isDirectory: function isDirectory(dir, cb) {
        fs.stat(dir, function (err, stat) {
            if (!err) {
                return cb(null, stat.isDirectory());
            }
            if (err.code === 'ENOENT' || err.code === 'ENOTDIR') return cb(null, false);
            return cb(err);
        });
    },
    realpath: function realpath(file, cb) {
        var realpath = typeof fs.realpath.native === 'function' ? fs.realpath.native : fs.realpath;
        realpath(file, function (realPathErr, realPath) {
            if (realPathErr && realPathErr.code !== 'ENOENT') cb(realPathErr);
            else cb(null, realPathErr ? file : realPath);
        });
    },
    readPackage: function defaultReadPackage(readFile, pkgfile, cb) {
        readFile(pkgfile, function (readFileErr, body) {
            if (readFileErr) cb(readFileErr);
            else {
                try {
                    var pkg = JSON.parse(body);
                    cb(null, pkg);
                } catch (jsonErr) {
                    cb(null);
                }
            }
        });
    },
    moduleDirectory: 'node_modules',
    preserveSymlinks: true
}

resolve.sync(id, opts)

Synchronously resolve the module path string id, returning the result and throwing an error when id can't be resolved.