TypeError:app.use(）需要中间件函数

这是我的server.js文件和api.js文件。我在排序函数中遇到了一个错误，我打算在该函数中根据js对象的属性搜索它们。事件架构具有名称、位置、价格、评级等属性。我试着按照他们的价格分类。

server.js

var express= require('express');
var bodyParser= require('body-parser');
var morgan = require('morgan');
var config=require('./config');
var app= express();
var mongoose=require('mongoose');
//var User=require('./database/user')
mongoose.connect('mongodb://localhost:27017/db',function(err){
    if(err){
        console.log(err);
    }
    else{
        console.log("connected!");
    }
});
app.use(bodyParser.urlencoded({extended: true })); //if false then parse only strings
app.use(bodyParser.json());
app.use(morgan('dev'));//log all the requests to the console
var api=require('./app/routes/api')(app,express);
app.use('/api',api);
app.get('*',function(req,res){
    res.sendFile(__dirname + '/public/views/index.html');
});   // * means any route
app.listen(config.port,function(err){
    if(err){enter code here
        console.log(err);
    }
    else{
        console.log("The server is running");
    }
});
module.exports = router;

api.js

var User = require('../models/user');
var Event = require('../models/event');
var config = require('../../config');
var secret = config.secretKey;
module.exports = function (app, express) {
    var api = express.Router();
    app.use()
    api.post('/signup', function (req, res) {
        var user = new User({
            name: req.body.name,
            username: req.body.username,
            password: req.body.password
        });
        user.save(function (err) {
            if (err) {
                res.send(err);
                return;
            }
            res.json({
                message: 'User created!'
            });
        });
    });
    api.get('/users', function (req, res) {
        User.find({}, function (err, users) {
            if (err) {
                res.send(err);
                return;
            }
            res.json(users);
        });
    });
    api.post('/eventfeed', function (req, res) {
        var event = new Event({
            name: req.body.name,
            location: req.body.location,
            description: req.body.description,
            price: req.body.price,
            rating: req.body.rating
        });
        event.save(function (err) {
            if (err) {
                res.send(err);
                return;
            }
            res.json({
                message: 'Event created!'
            });
        });
    });
    // utility function for sorting an array by a key in alpha order
    api.get('/sortby_price', function (err) {
        if (err) return err;
            // utility function for sorting an array by a key in parsed numeric order
        else {
            function sortArrayNum(arr, key) {
                arr.sort(function (a, b) {
                    return parseInt(a[key], 10) - parseInt(b[key], 10);
                });
            }
            var dicts = EventSchema.saved;
            for (var i = 0; i < dicts.length; i++) {
                var terms = dicts[i].terms;
                sortArrayNum(terms, "price");
            }
        }
        return api;
    });
}

这是我的错误。我第一次用这个制作网页。请帮我这个错误告诉什么。

类型错误：app.use((需要中间件功能
在EventEmitter.use(c:''Users''MY APY''WebstormProjects''Main''node_modules''express''lib''application.js:209:11(
在module.exports(c:''Users''MY LAPY''WebstormProjects''Main''app''routes''api.js:10:9(
在对象处。(c:''Users''MY LAPY''WebstormProjects''Main''server.js:20:36(
在模块中_compile(module.js:460:26(
位于Object.Module_extensions..js(Module.js:478:10(
在Module.load(Module.js:355:32(
在Function.Module_load(Module.js:310:12(
位于Function.Module.runMain(Module.js:501:10(
启动时(node.js:129:16(
在node.js:814:3