require NodeJS

app.js
------

// ...
var controllers = {};
controllers.foo = require('.controllers/foo');
controllers.bar = require('.controllers/bar');
app.get('/api/foo', controllers.foo.index(req, res));
app.get('/api/bar', controllers.bar.index(req, res));
//..
//start server


controllers/foo.js
------------------
//..
var filters = {};
filters.alpha = require('.filters/alpha');

exports.index = function(req, res) {
    //..
    filters.alpha(..);
    //..
});


How may times would alpha be required once the server has started? Is it required everytime a client requests for /api/foo ?