node/tools/eslint/node_modules/resolve/lib/node-modules-paths.js

var path = require('path');
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
    start = path.resolve(start);

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

    var paths = [start];
    var parsed = parse(start);
    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;
};