node-modules-paths.js

var path = require('path');
var fs = require('fs');
var parse = path.parse || require('path-parse');

module.exports = function nodeModulesPaths(start, opts) {
    var modules = opts && opts.moduleDirectory
        ? [].concat(opts.moduleDirectory)
        : ['node_modules'];

    // ensure that `start` is an absolute path at this point,
    // resolving against the process' current working directory
    var absoluteStart = path.resolve(start);

    if (opts && opts.preserveSymlinks === false) {
        try {
            absoluteStart = fs.realpathSync(absoluteStart);
        } catch (err) {
            if (err.code !== 'ENOENT') {
                throw err;
            }
        }
    }

    var prefix = '/';
    if (/^([A-Za-z]:)/.test(absoluteStart)) {
        prefix = '';
    } else if (/^\\\\/.test(absoluteStart)) {
        prefix = '\\\\';
    }

    var paths = [absoluteStart];
    var parsed = parse(absoluteStart);
    while (parsed.dir !== paths[paths.length - 1]) {
        paths.push(parsed.dir);
        parsed = parse(parsed.dir);
    }

    var dirs = paths.reduce(function (dirs, aPath) {
        return dirs.concat(modules.map(function (moduleDir) {
            return path.join(prefix, aPath, moduleDir);
        }));
    }, []);

    return opts && opts.paths ? dirs.concat(opts.paths) : dirs;
};