Events

app.on(‘mount’, callback(parent))

当子程序被挂载到父程序时，mount事件被发射。父程序对象作为参数，传递给回调方法。

var admin = express();
admin.on('mount', function(parent) {
    console.log('Admin Mounted');
    console.log(parent); // refers to the parent app
});
admin.get('/', function(req, res) {
    res.send('Admin Homepage');
});
app.use('/admin', admin);