node js find file up from current location into file system until user home dir or top level dir

lookup.js

/*jshint node:true*/
var
    path = require("path"),
    fs = require("fs"),
    userhome = path.resolve(process.env.HOME || process.env.HOMEPATH || process.env.USERPROFILE),
    out;

function lookup(filename) {
    var lookupd = process.cwd(),
        isFile,
        fullpath;

    function isGoodToGoUp() {
        var
        isUserhome = (lookupd === userhome),
            _lookupd = path.resolve(lookupd + "/../"),
            isTop = (lookupd === _lookupd),
            gtg;

        isFile = (fs.existsSync(fullpath) && fs.statSync(fullpath).isFile());
        gtg = (!isFile && !isUserhome && !isTop);
        lookupd = _lookupd;
        return gtg;
    }

    (function traverseUp() {

        fullpath = path.resolve(lookupd, filename);

        if (isGoodToGoUp()) {
            traverseUp();
        }
    }());

    return isFile ? fullpath : null;
}

out = lookup(".npmrc");