fs.realpath()

fs.realpath(path[, cache], callback)

Asynchronous realpath(2). The callback gets two arguments (err, resolvedPath). May use process.cwd to resolve relative paths. cache is an object literal of mapped paths that can be used to force a specific path resolution or avoid additional fs.stat calls for known real paths.

Example:

var cache = {'/etc':'/private/etc'};
fs.realpath('/etc/passwd', cache, (err, resolvedPath) => {
  if (err) throw err;
  console.log(resolvedPath);
});