Routing in Node & Express: app.use does not work unless full path is provided

I have the following setup:

我有以下设置：

app.use('/', rootRoute);
app.use('/wiki', wikiRoute);

/// default handler
app.use(function(req, res, next) {
    var err = new Error('Not Found');
    err.status = 404;
    next(err);
});
app.use