app.post('/signUp', userController.signUp);

var userController = require('./routes/userController');

exports.signUp = function(req, res, next) {
    api.saveUser(req.body).then(function(result){
        res.redirect('/');
    }).catch(function(err){
        if (err.toJSON().code === 11000){
            res.status(500).send("This email already exist")
        }
    })
};

Error: Route.post() requires a callback function but got a [object Undefined]
        at Route.(anonymous function) [as post] (D:bsuir3 курс1 семnodeappnode_modulesexpresslibrouterroute.js:202:15)
        at Function.app.(anonymous function) [as post] (D:nodeappnode_modulesexpresslibapplication.js:482:19)
        at Object.<anonymous> (D:nodeappserver.js:61:5)
        at Module._compile (module.js:635:30)
        at Object.Module._extensions..js (module.js:646:10)
        at Module.load (module.js:554:32)
        at tryModuleLoad (module.js:497:12)
        at Function.Module._load (module.js:489:3)
        at Function.Module.runMain (module.js:676:10)
        at startup (bootstrap_node.js:187:16)
        at bootstrap_node.js:608:3