As of Express 4.x, the directory middleware is no longer bundled with express. You’ll want to download the npm module serve-index.
Then, for example, to display the file/dir listings in a directory at the root of the app called videos
would look like:
var serveIndex = require('serve-index');
app.use(express.static(__dirname + "https://stackoverflow.com/"))
app.use('/videos', serveIndex(__dirname + '/videos'));